CA1130603A - Optical method for remote determination of the geological nature of a homogeneous surface - Google Patents

Abstract

IN THE UNITED STATES PATENT AND TRADEMARK OFFICE

APPLICATION
OF
CHARLES W. KOUNS
FOR
OPTICAL METHOD FOR REMOTE DETERMINATION OF THE
GEOLOGICAL NATURE OF A HOMOGENEOUS SURFACE

ABSTRACT OF THE DISCLOSURE

An optical method for identifying an immobile target having a homogeneous surface is disclosed. Light reflected from the surface of the target is electro-optically detected. The Stokes parameters of the detected light are measured in four preselected, adjacent, spectral bands. A discrete value termed the polarization intensity index (PII) is calculated using the measured Stokes parameters. Each homogeneous surface has a characteristic PII value. Substantially identical surfaces display substantially identical PII values. By comparing PII
values of unidentified target surfaces with a set of previously determined PII values for different, known target surfaces, the geological nature of an unidentified target surface may be determined.

S P E C I F I C A T I O N

Description

Kouns~ 306~3 ~, I .

1. Field of the Invention 3 This invention relates in general to the 4 detection and analysis of reflections of a regular translational source of electro-magnetic wave radiation ~ -6 from preselected, unidentified, target surfaces. More 1 7 particularly, the present invention relates to a method 8 for the remote identification of a preselected, unidentified, -homogeneous target surface.

2. Description of the Prior Art 11 It is known in the literature that the Stokes 12 parameters of light emerging from the top of the earth's 13 atmosphere may be predicted as a function of sun angle -14 ¦ and viewing angle when viewing extensive areas of the earth over which the reflecting and polarizing properties 16 are reasonably uniform. These predictions depend on 17 detailed measurements of reflecting and polarizing 18 properties of various materials, such as sand, clay and 19 grass, when illuminated by sunlight. See Final Report "Experiment SO46:Visible Radiation Polarization 21 Measurements:Phase C," NASA DOC. NAS9-7267, page 1, 22 January, 1968. See also Oetken, "Polarimetric Methods -23 in-Astrophysicsll JENA REVIEW, Vol. 15, page 330, June, 24 1970, w~ich describes that to obtain the physical conditions of objects, the radiation from these objects is converted 26 to Stokes parameters from which the degree of polarization 27 (intensity), polarization directions, etc. is determined.
28 Moreover, there is described in an article by 29 I Cacciani and Fofi, "A Complete Stokes-Meter," Solar Physics, 30 I Vol. 19, pp. 270-276 (1971), apparatus for measurîng Kouns~ 30 ~ O 3 1 I Stokes parameters resulting from incident and reflected 2 ¦ radiation. Also taught by Cacciana and Fofi is that the

3 state of partially polari~ed radiation may be determined

4 by the use of (1) azimuth determination, (2) its intensity and (3) the non-polarized background.
6 However, heretofore, remote sensings of target 7 -surfaces have been conducted with polarimetry on a limited 8 basis in specialized applications. General applications 9 to ground truth, with remote sensings of reflected light, have faltered on three technical impediments: (1) there 11 was no imaging polarimeter in being; (2) no simple procedure 12 existed for evaluation of the intrinsic polarization 13 intensity of a target surface as distinguished from the 14 optical thickness between a light source and target surface as well as from a target surface through recording;
16 and (3) there was no discrete index to gauge the correlation 17 of data because of the stochastic character of optical 18 waves in thin film phenomena. Consequ~ntly, in view of 19 the fact that polarization is a stress sensitive parameter of light, interfacial dynamics under natural conditions 21 have tended to mask polarization signatures of target 22 surfaces. This masking effect and the stochastic 23 characteristics of optical waves have impeded the 24 development of i~aging poIarimetry BRIEF SUMMARY OF THE INVENTION
26 1. Obiects of the Invention 27 It is an object of this invention to provide 28 ¦ a method for identifying the geological nature of a 29 ¦ homogeneous target surface employing remote sensing means.
~ : Another object of this invention is to provide ~ , , " , i l~ l $

Kouns- 1 1 li3V603 . ' ' i, 1 an improved method of remote sensing of surfaces as to 2 homogeneity and location.
3 An object of the present invention is to 4 provide an improved method of remote sensing of surfaces as to horizontal or vertical orientation. -6 Another object is to pro~ide an improved method 7 of remote sensing of target surfaces as to optical thick-8 nesses not intrinsic to the target surfaces.
9 Still another object is to provide an improved method of remote sensing of surfaces as to indexing 11 stochastic averages for correlation of data.
12 An object of this invention is to provide an 13 improved method of recording polarization of reflected 14 light to determine precise correlation of measurements employing reflected sunlight.
16 Another object is to provide an improved method 17 of discrimination with polarimetry to determine surface 18 homogeneity of horizontal or vertical targets of interest -employing reflected sunlight.
These and other objects and advantages will 21 readily become apparent to those skilled in the art in 22 the light of the te~chings hereinafter set forth.
23 2. Definitions 24 By "ground truth" as used throughout the specifi-cation is meant the natural discrimination between various 26 terrain surfaces due to their inotrin~ic compositions such 27 as sand, clay and rock. Such surfaces may be masked by 28 I vegetation, residuals of erosion and decomposition.
29 ~ Thus, in general, "ground truth" is a delineation of a 30 , natural surface of the earth. Remote sensing of target Kouns-l . .

1 surfaces according to this invention encompasses man-2 made surfaces as well as spontaneous surfaces exhibited 3 by nature. "Ground" tends to be restrictive to the planet 4 earth whereas "surface truth" embraces the cosmos in the sense of space. Moreover, the target could be a 6 particle, a suspension, a thin slice or surface of an 7 inorganic or organic substance. Consequently, surfaces ~ I are referred to in this application in their broadest 9 connotation, i.e., "surface truth". ¦ -By "stress sensitive" as used throughout the 11 specification is meant that a target may exhibit a 12 ¦ static equilibrium or dynamical equilibria due to its 13 intrinsic composition be it simple and/or complex, and, 14 as modified by any physical and chemical stresses acting thereon such as heat, loading, moisture, crystallization 16 both internally and adjacent thereto. For example, 17 quartz has "optical activity", i.e., the ability to rotate 18 the plane of polarization of light. ~his ability may 19 be influenced by mechanical stress and by heat which causes piezocresence or changes in the anisotrophy of 21 crystalline material and other changes in amorphous material.
22 I quartz is stressed beyond its elastic limit, it could 23 have a rupture or a permanent set. With a smaller stress, 24 the quartz could continue to have upper and lower limits o~ stress depending on the dynamics of its environment 26 and its relation thereto. Also, time may be an important 27 factor, especially in geological phenomena.
28 For example, if a remote sensing means of this 29 invention is situated in a satellite which traverses in its orbit a region where qu~rtz is unstressed, an adjacent I' , ,, `;ouns- 1 l 1¦1 region where the quartz is stressed and then a region 2 where the quartz is unstressed, the spectral signatures 3 of the two unstressed quartz occurences might be about 4 equal. However, the spectral signature of the strained quartz might be different because the inherent polariz-6 ing character of the stressed quartz might result in more 7 ~ or in less reflected and/or radiant energy reaching the 8 scanner and being recorded when compared with the reflectants 9 and/or radiations from the unstressed quartz. The eye or standard camera might not recognize this difference.
11 However, the remote sensing means of the present invention 12 as described more fully subsequently herein can discern 13 this differentiation. Although quartz has been used as 14 an example herein because of its abundance in nature and 15 ¦ its diverse allotropic forms, there are many other materials 16 existing in nature which will exhibit their intrinsic 17 polarization signatures in both simple and complex aggrega-18 tions as modified by stress. ¦ ;
19 By "look angles" as used throughout the specifica-tion are meant the orientations of the remote sensing means 21 to intercept ~he reflected and/or radiated energy from 22 a target. For horizontal targets, a vertical look angle 23 is equal to the angel of elevation of the sun above the 24 horizontal plane of the remote sensing means when surveyed in its operating position. It approximates the nadir 26 angle of the sun to the elevation of the remote sensing 27 means. However, since the angle of reflection on a target 28 l~ is equal to the angle of incidence from the light source, 29 l the remote sensing means is depressed by this angle below 30 l the horizontal plane of the remote sensing means to intercept ~3[)6(33 Kouns~ ç

1¦l the reflected energy. The horizontal look angle is equal 2 ¦¦ to the angle of azimuth of the sun measured from true 3 i north clockwise to the remote sensing means - sun line of 4 sight at the remote sensing means. For vertical targets, the "look angles" are different as indicat~d subsequently herein.
71 By "optical waves" as used throughout the 1 81 specification is meant those waves reflected and/or 9 ¦ radiated by the full range of the electromagnetic 1~¦ spectrum.
By "remote sensing" is meant the science 12 l¦ and art of acquiring information about material things 13 ,¦ from measurements made at some distance without direct 14l physical contact of those things.
15 ¦ By "radiation" is meant the emission and 16 ¦ propogation of energy through space or through a material 17¦ medium in the form of waves.
18 3. ~rief Description of the Inventio~
19 ¦ It has now been found that a relatively simple and effective optical method is provided for remote 21 identification of the geological nature of homogeneous 22 1 target suriaces. The nature of a target surface composi-23 ¦ tion, such as part of the earth's terrain, can be 24 1 remotely sensed, analyzed and identified geologically 25 ¦ according to the present invention. The surface may be ~6 ¦ either stationary or moving relative to the remote 27 1 sensing system.
28 1¦ A remote sensing means, preferably consisting 29 l of a polarimeter, is employed to sense reflections of a regular translational source of electromagnetic wave ~L~3~1603 Kouns-l ¦

1I radiation, such as the sun, from the surface of the 2 ¦¦ target to be geologically identified. The remote 3 sensing means should be stationary with respect to the 4 target at the time when readings are taken to avoid S spurious data being collected. In one embodiment of 6 the present invention, the remote sensing means is mounted 7 to a transit base rigidly positioned above the earth 1 8 and within its atmosphere. In another embodiment, the 9 remote sensing means is mounted to a transit base which base is rigidly positioned exterior of the earth's 11 atmosphere, such as in an orbiting satellite. ¦ -12 In either of the two embodiments discussed 13 hereinabove, the remote sensing means is aimed directly 14 at the sun and elevation and azimuth are sensed and recorded. The remote sensing means is then aimed at ¦ -16 the ground at the same azimuth and at a depression 17 angle equivalent to the formerly recorded elevation 18 angle. The target is then defined by the area around 19 - the line intercepting the ground. The objective is to have the remote sensing means receive reflected light 21 directly from the sun.
22 According to the present invention, it 23 has been found that a target area between about 24 ~ foot and about 2 feet in diameter may be identified as to its geological nature by use of the remote ~6 sensing means. When substantially horizontal targets 27 are desired to be identified, it has been found that there 28 ¦I should be about 40 meters in distance between the I -29 1! remote sensing means and the target per 2 meters in 30 l~ diameter of the horizontal target. This rule of thumb ouns- 1 . ~3~603 . 1, l applies to the embodiment of applicant's invention wherein 21 the remote sensing means is fixedly mounted to a base 3 situated within the earth's atmosphere. In the embodi- ! ,, 4 ment of applicant's invention wherein the remote sensing means is mounted to a base situated exteriorly of the 6 I earth's atmosphere, it is believed that there should 1 7 be about 20 kilometers in distance between the remote 8 sensing means and the target per 1,000 meters in 9 ¦ diameter of the horizontal target.
As indicated previously herein, the remote 11 sensing means with a nadir orientation intersecting a 12 truly horizontal surface would cover a circle of 1 foot 13 diameter for each 20 feet of elevation above the horizontal 14 surface. This ratio and other ratios previously described herein can be modified, if desired, by engineering design 16 of the remote sensing means to the resolution desired.
17 The resolution can thus be adjusted by proper selection 18 of the wavelengths of energy being sensed. In the visible 19 region, the wavelengths are on the order of 0.001 cm, while in the microwave region, the wavelengths are on 21 the order of whole centimeters.
22 When a substantially horizontal surface is : 23 targeted using a polarimeter as the remote sensing 24 means 7 the target is typically quasi-circularly shaped.
When a substantially vertical surface is targeted using 26 a polarimeter as the remote sensing means, the target 27 is circular in shape.
28 The remote sensing means is designed to filter 29 received light into four preselected wavelengths~
30 ,I through ~ ~, and read out t~e Stokes Parameters Q,U and _g_ .~uns- 1 1 . .. 1~L30~1~3 -, 1 I for each of the preselected wavelengths, from which aj -2 I polarization intensity (PI) for each preselected 3 wavelength can be derived. For targets comprised of 4 a homogeneous surface, it has been found empirically that conjugate bands (~ ) in a given spectrum will have the 6 same value of PI as will be the case with the conjugate 7 bands (~n~ ~) in a diferent spectrum. It has also .
8 been discovered that the PI values for /~ +~will be 9 different than the PI values for~ and the relation-ship of that difference will vary from material to 11 material.
12 Moreover, it has also been discovered that if ¦ -13 the target is not homogeneous, the PI values for all 14 four preselected wavelengths,~ through~ ~3will vary.
The relationship of the dif~erence in PI values between L6 conjugate bands in two spectra defines a polarization.
17 intensity index (PII) which, in effect, is a characteristic 18 signature of a homogeneous suface. By comparing and l9 correlating known PII values with measured PII values of unidentified target surfaces according to this invention, 21 it is possible to identify the geological nature of a 22 homogeneous target surface via remote sensing means.
23 The features that characterize the novelty of .
24 the present invention are set forth with particularity in the appended claims. Both the organization and manner 26 of operation of the present invention, as well as other 27 objects and advantages thereof, will be apparent by reference 28 ¦ to the detailed description which follows taken in 2g I conjunction with the accompanying drawings wherein like 30 1I reference symbols designate like parts throughout the figures I ``

ouns~ 13~603 1 thereof.

2' BRIEF DESCRIPTION OF THE DRAWINGS
' !
3 , Fig. 1 is a schematic diagram of an embodiment 4 of a polarimeter apparatus for carrying out the present invention for substantially horizontal targets.
6 Fig. 2 is a schematic diagram of another 7 embodiment of a polarimeter apparatus for carrying out 8 ¦ the present invention for substantially vertical targets.
9 I Fig. 3 is a graph schematically illustrating ¦ -10 i the relationship of reflection and radiation as a function ~ of wave length to show the null point of amplitude.

12 ¦ DESCRIPTION OF THE PREFERRED EMBODIMENTS
13 ¦¦ As understanding of the underlying concepts 14 ¦ associated with the present invention is necessary to an appreciation of the function of the remote sensing 16 means of the present invention, the following discussion 17 includes references to well-understood principles of 18 optics which form par~ of the basic fo~ndation of 19 applican~'s invention.
Based upon empirical measurements in the 21 laboratory, applicant has found that fixed illumination 22 of a target surface (passively as by a rigidly oriented 23 lamp or actively as by a sun-synchronous orbiting 24 satellite platform) has the practical effect of simulating 25 I a single optical plate which exhibits thin film character-26 ¦ istics of reflection and refraction by Fresnel's Laws.

27 ~l Under these conditions, polarization intensities of 28 I homogeneous target surfaces are distinctive for adjacent 29 1I spectral bands in the system as if each band were indepen-30 "~ dent of the other bands. .
.

~.~ 3~

Kouns~

1I Based upon further empirical measurements 2 ~l outside of the laboratory (in the field), applicant 3 ¦I has further found that regular translational illumination 4l of a target surface (passively as by the sun or actively as by controlled ar~ificial light) has the practical 6 effect of slicing the target surface into a statistical 1 7 array of parallel-adjacent optical plates each of which 8 !l exhibits thin film characteristics of reflection and 9 ¦ refraction by Fresnel's Laws. Under these conditions, ¦ -10 ll polarization intensities of homogeneous target surfaces are ~ equal for conjugate pairs of adjacent spectral bands in the 12 I system. The conjugate pair grouping is different for substan- ¦
13 ~ tially horizontal target surfaces and for substantially 14 ¦¦ vertical target surfaces. Also, the magnitudes of polarization intensities differ for different pairs of spectral bands in 16 the system.
17 In brief, applicant has discovered that the polariza-18 tion intensities of substantially homogeneous target surfaces 19 - are constant when they display the same thin film characteristic s of reflection and refraction by Fresnel's ~aws under identical 21 conditions. Interference spectroscopy of a target surface, 22 ¦ studies with regular translational illumination, will yield 23 ¦ results dependent on the translational speed of the illumina-24 tion providing all other pertinent factors remain unchanged.
Thus, within the limits of instrument precision, a generally 26 ¦ horizontal target surface which is optically homogeneous, 27 ¦! in terms of thin film characteristics of reflection and 28 ¦~ refraction, will exhibit virtually the same polarization 29 ' intensities tinder solar lighting in different states of 30 I the United States or in different countries of the world Xouns-l 1130f.;03 . I
1 providing other pertinent factors remain unchanged. These 2 pertinent factors include target latitude. The same logic 3 applies equally to a generally vertical target surface and to 4 target surfaces oriented between the two extremes of vertical and horizontal.
6 Thus, applicant's invention is based upon the dis- ¦
7 covery that optically homogeneous target surfaces have dis-8 tinctive interference signatures for their orientations as well 9 I as for their substance. In other words, all surfaces may be 10 I identified as to their substance and orientation whenever 11¦ regular translational illumination passes over them and is 12l reflected back as modified by the thin film characteristics 13¦ of all the boundaries involved. The complexities of evaluating~
14 all the boundaries involved may be appreciated from a considera-¦
tion of the well~known complexities involved in the performances 16 of thin-film optical devices from a qualitative viewpoint since 17 according to applicant's invention, target surface behavior 18 analogs that of thin-film optical devlces. For example, 19 H.A. McLeod in "Thin Film Optical Filters", American Elsevier Publishing Company, Inc., New York, 1969, at page 4 lists 21 several factors involved in understanding in a qualitative way 22 the performance of thin-film optical devices as follows:
23 l)The amplitude refle~tance of light at any boundary between 24 two media is given by (I-p)(I+p); where p is the ratio of the refractive indices at the boundary (the intensity reflectance 26 is the square of this quantity; 2)There is a phase shift of 27 ¦ 180 when the reflectance takes place in a medium of lower , 28 ¦ refractive index than the adjoining medium and zero if the ?
29 ¦ medium has a higher index than the one adjoining it; 3)If 30 1¦ light is split into two com~onents of reflection at the top and i " ~13(~603 bottom surfaces of a thin film, then the beams will recombine in such a way that the resultant amplitude will be the difference of the amplitudes of the two components if the relative phase shi~t is 180, or the sum of the amplitudes if the relative phase shift is either zero or a multiple of 360. In the former case, the beams are said to interfere destructively and in the latter case constructively. Other cases where the phase shift is different will be intermedlate between these two 10 - possibilities.
A review of optical principles dealing with interference is found in Drude, P., The Theory of Optics (Translated from the German by C. Riborg Mann and Robert A. Millikan), Dover Publications, Inc., ~.Y., 1959, pages 130-134. The optical train of the remote sensing means, the photo~polarimeter, of applicant's invention can be compared with the optical train of the Fresnel Mirror Experiment set forth in Drude, supra to rationalize the interference spectroscopy. However, Fresnel's experiments ~ 20 did not relate to regular translational illumination.
- With regular non-translational illumination, polarization intensity measurements of various targets have been influenced by six factors: the elevation and azimuth angles of the illumination source of the target; the spectral wave leng~hs employed in the measurements; and, the condition of the target surace being measured. Also, it is known that each wave band displays its own polarization intensity for each target as if it were alone.
However, according to applicant's method r the number of variables for any one target have been reduced. Two polarization prisms situated in the remote sensing means of mb/~b - 14 -~ .

~L~3(~603 I.Couns-l ~
I , ,, 1 ¦ applicant's invention are set at 90 and 180, respectivel~, 2 from the vertical in a common plane. Thus, when the remote 3 sensing ~eans is employed for surveying, the polarizing prisms 4 therein are identically oriented for each target. Moreover, the elevation and azimuth of the look angle on the target are 6 oriented to the elevation and azimuth angle of the sun illumina 7 tion to maximize the target flux in the common vertical plane 8 intersecting the sun, the target and the remote sensing means.
9¦ Four spectral wave bands have been found to be stable in band-10l pass values and in constant speed of rotation parallel to the 11 plane containing the stable polarizing prisms. The wave bands ~
12 are~n-0.5-o.6~m;~ n~,-0.6-0.7~m;~2-0.7-0.8~ ; and~ t3-0.8-l.l~m. 1 -' 13¦ The look angles are constant for any one target. The illumina-¦ -14 tion angles may vary slightly due to the motion of the sun during the time(in seconds~of data sensing and recording on 16 any one target. The generally horizontal or vertical target 17 surface conditions of ground truth may be' assumed as constant 18 for the recording time employed, gene~rally in the order of 19 seconds. ~ -One set of readings takes about 1.3 seconds. In 6 21 seconds, 4 complete readings can be taken and recorded. If th~
22 remote sensing means were aboard a satellite hovering in space 23 at the time of recording, it would still take about 1.3 secondc 24 to complete one reading. This is due to the magnitude of difference between the speed of the sun and the speed of the ' 26 earth, i.e., 186,000 miles persecond to about 1,000 miles per 27 hour viz-a-viz the sun at the Equator. The speed of the earth¦
28 decreases gradually to zero at the r~spective Poles.
29ij The differential variability of the sun-source 30l,l illumination for a brief p~riod of time, generally in the ~13~6~)3 order of seconds and preferably up to about six seconds, by translational motion substantially satisfies Fresnel's-mirrors experiment for ~ and ~ +l as a conjugate pair and for ~n+2 and ~n+3 as a conjugate pair with near horizontal targets that are homogeneous at their surfaces. It is thus believed that statistical limits of destructive and constructive interference are induced by interaction of the mobile sun source flux on the polarizing prisms as conditioned by ground truth of the target for adjacent wave bands because the regular translational motion of the light source has the practical effect o -slicing--the target sur~ace into an array of parallel and adjacent plates. It is also believed that the flux from each plate includes rays from surface reflections plus waves from refracted re~lections~ The target media and their optical character determine what portion o~ the refracted beams emerge at the target surface and travel parallel to the surface reflections that escaped refraction. This -stream--`~ of parallel reflections is essentially an optical signature ~ 20 input into the remote sensing means of applicant's invention.
The remote sensing means discriminates the optical signature input in terms o~ its polarization intensities (PIs~ by means of the Fresnel-mirrors analogy.
Each homogeneous target which is substantially horizontal has associated therewith, under similar conditions, a polarization intensity index (PII~ signature according to the formula:

PIIH = PI~n,n+l-PI~n+2,n+3 PI~n,n+l+PI~n+2,n+3 mb/~ - 16 -~7i, Kou~s~
~1 ~
1 ¦ It is noted that PI ~ n~2,n+3 indicates that the spectra 2 1l ~ n+2 and ~ n+3 were observed to display equal polarization 3 intensities as a conjugate pair. The same is true for the 4 spectra ~ n and ~ n-~l. Minor differences in the index signatures for identical horizontal surfaces relate to breaks 6~ or masking of the homogeneity.
7¦ A similar rationalization applies for field targets ¦
8 1I which are substantially vertical. In such case, the con3ugate, 9¦¦ pairs are ~ n, ~ n+3 and ~ n+l, ~ n+2. Each homogeneous target which is substantially vertical has associated therewith, 11 under similar conditions, a PII signature according to the 12 formula: ¦ -13 PIIV= PI ~ n,n+3-PI ~ n+l,n+2 PI'~ n,n+3+PI ~ n+l,n+2 1 -14 ! --The autocorrelation of conJugate pairs of wave I -16 bands, since it renders all stress history in the system ¦ -17 common to the height of the remote sensing means above a 18 target, allows for surface correlations by comparisons despit~
19 the elevation o~ the instrument above the target surface.
Utilizing the method o applicant1s in~ention, land surfaces 21 may be accurately mapped with precise registration for 22 their instrinsic composition and orientation, including 23 vertical surfaces of canyons, wells and mines. Subtle 24 differences in ground truth associated with surface halos indicative of fossil fuels and other important minerals may 26¦¦ also be identified. Moreover, by employing polarimetry in 27l the range of Angstrom units (10-8c~), reflected light studies 28l, of natural and empirical microscopic specimens may be made 29,¦ according to applicant's invention. Other applications of 30 l applicant's method inclu~ the identification of crops and ~ . .. .. .

~OUDS- 1 . ,, 113(~603 Il . , ll range land. Because changes in elevation of the remote 2 sensing means of applicant's invention in the same region 3 of latitude do not impact the conjugate pair phenomena, 4 applicant's method, with its integration of variables in data results of the poLarization intensity, provides a 6 comparative calculus for deep space research by empirical 7 methods with resolution of surface areas adjusted by the 8 selection of instrument-target distances.
9 When the remote sensing means is mounted within an orbiting satellite, it is preferred that the orbit be 11 sun synchronous to avoid the Doppler effect for either a neari 12 horizontal target or a near vertical target. Such a system 13 negates the natural and regular translational illumination 14 in the system of applicant's invention. At the time of recording, a hovering satellite would be suitable for 16 sensing of near horizontal or near vertical surfaces.
17 However, the remote sensing means i situated aboard an 18 orbiting satellite, would need to incorporate transit l9 characteristics for "look angles" and precision. For near horizontal targets in applicant's method of remote sensing, 21 the rotation of the earth counter-clockwise on its axis in 22 the Northern Hemisphere (clockwise in the Southern Hemisphere 23 has the effect of algebraically decreasing the speed of 24 light impacting the target in the Northern Hemisphere (algebraically increasing the speed of light impacting 26 the target in the Southern Hemisphere.) For near vertical ¦
27 targets in applicant's method of remote sensing, the revolu- I
28 I tion of the earth counter-clockwise in its ecliptic about 29 ~ the sun in the Northern Hemisphere (clockwise in the 30 ¦I Southern Hemisphere) has the effect of algebraically . ~13~603 Kouns-l I

l!! decreasing the speed of light impacting the target in the 2 I Northern Hemisphere (algebraically increasing the speed of 3 ! light impacting the target in the southern Hemisphere).
4 In each instance, the Doppler Effect is intrinsically

5 ! corrected for by causing the adjacent filter bands in the

6 optical system to indicate equal amplitudes of reflected ~ -

7¦, Irradiation Flux and/or radiated energy whenever the target

8 1 is homogeneous. This is in accord with Fresnel's Laws

9 1l for thin films. If the target is not homogeneous in lOi` accordance with Fresnel's Laws, the adjacent filter bands ~ in the optical system indicate unequal amplitudes of reflectel -12,¦ Irradiation Flux and/or radiated energy.
13 ¦¦ Referring to Fig. 1, there is shown one embodi-14 li ment of an apparatus for carrying out applicant's invention.
The apparatus consists of a polarimeter 10 for geological 16 remo~e sensing, i.e.1 the determination of the nature of 17 a near horizontal earth surface composition by remote sens- ¦ -18 ¦ ing means. The polarimeter device~ is known as the "Visible ¦
19 Light Polarimeter-Lab. Type S046`' (commercially available ¦
from General Electric Company, Space Division, PØ Box 21 8555, Philadelphia7 Pennsylvania 19101). The S046 Type 22 Photopolarimeter is a scientific device intended to be 23 ~ used for the measurement of the Stokes parameters of a 24 I light flux in each of several-wavelength intervals of 25 ! light. The values of the Stokes parameters may be used 26 to calculate the degree of polarization of the light ¦ -27¦¦ flux. A more detailed description of the instrument is 28¦~ reported at the Ninth International Symposium on Remote ! `
29l' Sensing of Environment, April, 1974 or in "Visible Light 30l' Photopolarimeter SysteDI for Field Studies", General-Electric ,, ..

~.~30603 Il . . ,. ,. , . i Kouns-lI

1¦ Company, Space Division, Space Sciences Laboratory 2~ King of Prussia, Pennsylvania, January 5, 1977.
3 Light is received and transmitted through the 4 polarimeter to a light detector in each of three optical ¦
paths. Electrical signals generally internally in response 6 ¦ to this light are called B, D and ~I. They are related 7 I to two of the Stokes parameters, Q and U, as follows:
8 ~Q = B - ~I and ~U = D ~

- 10 I This subtraction is performed within the photopolarimeter -~ 10 and the output of the instrument is a continuous series 12 l¦ of pulses in which the values of Q, U and I in one ~` 13 wavelength band, are given by the magnitude of three 14 consecutive pulses, then the values of Q, U and I, for another band, are given etc. for each of the wavelength 16 bands and then the sequence returns to the first band 17 again. The Stokes parameters Q, U and I are related 18 by the following equations:
l9 I = total intensity of light Q = IP cos ~2x) ; 20 U = IP sin (2x) 1 21 Since cos2A ~ sin2A=l, P may be calculated :.
22 by the following equation:
23 . P = ~

251 The filter bandwidths employed according to applicant's I invention are as follows:
26 I t 1 0.5 to 0.6 micrometer t 27 j 0.6 to 0.7 micrometer 1 0.7 to 0.8 micrometer 28 ¦ 0.8 to 1.4 micrometer 29 ¦ Referring now to Fig. 1, there is shown a ¦

layer of sulfur 12 whose mean thickness and electrical Kouns~ 30603 I
I . .-l properties, in addition to the electrical properties of 2 a soil substrate 14 resting beneath it, are unknown.
3 Natural radiation from sun 16 is intercepted at the , 4 sulfur layer 12. Reflected energy from the top surface of the sulfur layer 12 is sensed by optical channels 6 18, 20, and 22 of the polarimeter 10 on a transit base t;
7 and directed in amplitude detectors 24, 26 and in wavelength .,-8'l detectors 28 the output of the wavelength detectors 28 g ! is fed to an analog recorder 30. The information received ;-10 i from the analog recorder 30 is analyzed in a computer , ll 1 32 to derive the polarization intensities of the filtered "
12 spectra according to the formula mentioned previously 13 ¦ herein. The outputs of the computer 32 corresponding ,~, 14 to the computed PI and PII are designated by the numerals 34 and 36, respectively. ,~
16 Analog ;ecorder 30 and programmable computer 17 32 are well-known commercial items and will not be described in ,,~
18 detail since they are not essential to the method of applicant's "
19 invention. ¦ -The S046 photopolarimeter 10 contains three 21~ optical channels 18,20 and 22. The channels 18, 20 r 22 contain Glan Thompson type polarizing prisms in the 23 focal region of the collimating lenses. Measurement t 24 of the Stokes Parameters: ~ I on channel 18, U on channel ~, 20 and Q on channel 22 are made by comparing the 26 orthogonal polarized beams 24 and 26 with the beam 18.
271 Comparison of the beams is effected by an electro- , 281 mechanically driven beam selector wheel (not shown) 29il which is placed in the focal plane of the t,hree collimating 30~1 lenses. The Glan Thompson t,~pe,prisms are oriented to .. . .
! 21 Kouns-l ~
il, ! -1~l accept light polarized at angles of 90 (beam 24) and 2~l 180 (beam 26) from the vertical. These polarized 3 components are designated B and D, respectively. The 4 parameters Q and U are obtained as the differences I-2B and I-2D. Between the two channels 18,20 with the 6 prisms in the same common plane (perpendicular to the 7 longitudinal axes ~f the channels) are windows which 8 1l pass light flux being reflected by the target surface. ~ -9¦1 The channel 18 is labeled ~ (I).
10l¦ To the rear of the fixed B-D-I plane 20, 22 and 18, there is fitted a parallel rotating plane 28 12 ¦¦ with four spectral filters on a common arc in the order --13 ~ n+2=0.7-0.8 micromPters; ~ n+l=0.6-0.7 micrometers; -14 ~ ,n=0.5-0.6 micrometers; and ~ n+3=0.8-1.1 micrometers.
These filters pass the vertical and the horizontal 16 components in quadrature of polarized reflectance from 17¦ the target surface simultaneously for their respective 18 wave bands 28 concurrently with the free flowing light 19 flux 18 reflected from the target. The timing is geared to a Geneva movement so that one complete pulse of all 21 four bands 28 is cycled in 1.3 seconds. This provides 22 a coded print-out Q, U and ~(I) for each of the four 23 spectral bands 28. These terms are known as Stokes 241 parameters for polarized light. They are converted .
251 to a polarization intensity 34 expressed as a percentage by -26¦ solving the equations for each wave band, respectively, 27~ according to the formula:
28 ~ PI ~ n,n+l,n+2,n~3=100 30l The polarimeter 10 is preferably fitted to a Koun s -1 l i3~603 l¦i biaxial yoke (not shown) with a transit style mounting 21; to facilitate precise orientation and registration of 3 I traverses by latitude and longitude. In addition, the 4 ~ case (not shown) of the polarimeter 10 is fitted with a 5 ¦ gun sight telescope and sun shield for manual tracking 6 ¦¦ of the sun and other targets. The polarimeter 10 is linked 7 ¦¦ by a cable (not shown) to a central control panel (not) -8 1I shown) and electronics package (not shown) powered by a portable 12V storage battery unit wi~h an AC inverter 10 l and a constant voltage source. The control panel is -

11 1 linked by a cable to a recorder 30 that prints out

12 1I Q, U and ~ I values cyclically in 12 coded line pulses ¦~ by band sequence 0.7-0.8 micrometers on line 31A ( ~ n~2);
14 ¦ o.6-0.7 micrometers on line 31B ( ~ n~l); 0.5-0.6 15 ¦ micrometers on line 31C ( ~ n); and 0.8-1.1 micrometers 16 on line 31D ( ~ n+3).
17 In operation, the polarimeter 10, mounted 18 on a rigidly positioned transit base, ~is ai~ed directly 19 at the sun and elevation and azimuth angles are recorded.
The polarimeter 10 is then aimed at the ground at the 21 same azimuth angle and at a depression angle equivalent 22 to the formerly recorded elevation angle. The target 23 is then defined by the area around the line intercepting 24 the ground. The objective is to have the polarimeter receive reflected light directly from the sun.
26 The polarimeter 10 filters received light in 27 four wavelengths ~ n through ~ n+3, and the recorder 30 281 reads out the Stokes parameters Q, U and ~ I 33 for 2911 each of the wavelengths ~ n through ~ n~3, respectively, I
30~ on lines 31A to lines 31D, respectively. Polarization - ' .. 113UI;03 Kouns-l ¦

1~l intensity (PI) for each wave length, ~ n through ~ n+3 2~ respectively, as we.ll as a polarization intensity index 3 (PII) for the target, can then be derived in computer ~ 4 32 as discussed previously herein. For homogeneous 1 5 material targets, conjugate bands ~ n,n+l in a given 1 6 spectrum will have the same PI value as is the case with ` 7 conjugate bands ~ n+2,n+3 in a different spectrum. The ¦ -8 ¦¦ PI values for ~ n,n+l will be different than the PI
values for ~ n+2,n+3 and the relationship of the 10l difference will vary from material to material. If 11¦ the target is not homogeneous, ~ n through n+3 values 12¦ will all vary with respect to one another. -3l Referring to Fig. 2, the polarimeter 10 is 14l¦ shown in use for geological remote sensing of the 15 ¦ nature of a substantially vertical earth surface 16 composition. The polarimeter 10, again mounted on a 17 rigidly positioned transit base, is aimed directly at 18 the sun and elevation and azimuth angles are recorded.
l9 The polarimeter 10 is then aimed at the ground at ; 20 the same azimuth angle increased by 180 and at an 21 elevation angle equivalent to th~ formerly recorded 22¦ elevation angle. Targets on an east surface need an 231 afternoon sun and a downward traverse. Targets on a 24l west surface need a morning sun and an upward traverse.
2s1 Operation of the polarimeter 10)recorder 30 and computer 26l 32 is then the same as described previously herein 27 1l with respect to the embodiment of Fig. 1. For homogeneous 2811¦ targets, conjugate bands ~ n+l,n+2 in a given spectrum !!~ will have the same value of PI as will be the case with 29'l !
0ll conjugate bands ~ n,n+3 in a different spectrum. The PI

Kouns- l . . . 1130603 Il . I ,,, 1 1 values for ~ n+l,n~2 will be different from the PI
2 ! values for ~ n,n+3 and the relationship of the difference 3 will vary from material to material If the vertical 4 target is not homogeneous, ~ n through n+3 PIs will all vary.
6 The accuracy of the photopolarimeter 10 is 7 sensitive to changes in the light irradiation incident ¦ -8 I on its collecting lenses due to possible motion of the 9 I polarimeter 10. Consequently, the photopolarimeter 10 1 .
10 1 should be immobile and stationary although the photo- I -11 polarimeter 10 may be allowed to move relative to the I -12 target surface such as in a satellite orbit about the earth.

13 The invention is not limited to the use of

14 I natural sunlight. Artificial illumination such as

15 I by linearly polarized light incident on the target

16 I surface may be employed.

17 The definition of surface does not preclude

18 penetration into the refIecting material to some extent.

19 While various modifications and variations have been suggested in the course of the description, it 21 should be pointed out that the invention is not 22 limited in scope to the specific embodiments described 23 or suggested. For example, radiations of different 24 wavelengths such as cosmic rays, gamma rays, x-rays, ultra violet below 4000~, infra red greater than 7000R, 26 Hertzian waves beyond 2.2x104 and the like may be 27 employed .
28 In the consideration of the band selection - 29 ,~ for polarimetry measurement according to the present 30 ~ invention, the factors discussed hereinbelow should ~ .

~L~3~603 ~Kouns~
be considered. In a controlled and relatively stable 2 11 system (as in a vacuum with standard temperature and 3 pressure) attenuation of Irradiance (I) is a natural 4~ straight line function that generally increases with 5 ¦ increasing wave lengths. By irradiance is meant the 6 radiant power incident on a surface and by attenuation 7 is meant the intensity loss of radiation according to 8 Lambert's Law. There are some interruptions in the 9 1 sy~metry of the straight line function of Irradiance attenua-tion, especially at sea level, but less so outside of 11 the earth's atmosphere. This lack of symmetry is 12 small at 0.5-0.6 microns ( ~) and at 0.6-0.7 microns (~
13 ¦ large but narrow at Q.7-0.8 microns(~ ~; and large at 14 0.8-1.1 microns (~t~) The variances in symmetry are generally 16 ! internal to applicant's four spectral bands. If such 17 ~ regularly decreasing irradiance, I, is impacted by any 18 , stress, the irradiance should change depending upon the 19 pertinent vectors and the degrees of freedom in the system. I~ a stress, such as the Doppler Effect, were 21 uniformly applied, its differential values would parallel 22 the attenuation slope. Such a result would be achieved 23 with a homogeneous target stressed under identical conditions. .' 24 Departures from such parallelism would indicate heterogeneity.
25 I The intensity would be proportional to the calculus slope 26 ¦ derivative of the spectra affected. PI can be considered 27 il as a concomitant of attenuation because, in general, 28l, the longer the wavelength, the greater the polarization.
29 In brief, as natural attenuation takes place by wavelength, 30 l polarization increases or decreases as the wavelengths ~- Kouns-l 1 I . ~1 l increase or decrease, respectively. Under homogeneous ' 2 conditions, i.e., equal refractive indices and identical 3 conditions, attenuation and polarization will be related 4 and equal respectively for light reflected by Fresnel's Laws even when the refractive index is complex. This 6 relationship will hold for all wave length segments whose 7 natural and intrinsic attenuation by wave length is a 8 !! straight line function. In this connection, the relative 9 ¦1 ease of reading of irradiance amplitudes in the visible 10 ¦ portion of the electromagnetic spectrum offers an advantage.
11¦ However, any other segments of the electromagnetic spectrum 12 could be used under natural and/or suitable empirical 13 conditions according to the method of this invention.
14 I In the visible segment of the electromagnctic spectrum, up to about 2.5 micro-meters, the attenuation 16 curves increase ~or clouds and molsture in the atmosphere.
17 However, the slopes of these curves have a general parallelism ¦
18 which can be detected by suitable telemetry of the respective 19 amplitudes of Irradiation Flux. Adverse stresses such as smog or pollution, if mutual to the optical elements of the 21 system, need not interfere with the correlative values of the 22 amplitudes directly recorded by wave lengths with good 23 linearity. Light is either absorbed by particles suspended in 24 ¦ the atmosphere such as dust, haze, smog,fog or rain and then is, emitted in all directions (true scattering), or light is 26 simply reflected by the surface of the particle. Scattering 27 diverts some of the light from the target so that it does not ~ -28 I enter the collector of the remote sensing means, or diverts 29 light that is not part of the target being observed into the 30 ¦ collector of the remote se~sing means. The result in either ~ j ~3~3 Kouns-l l , ~ ' , ¦ case is a reduction in contrast. This contrast reduction, 2 I often specified numerically in terms of a modulation transfer i 3 function, is caused by scattering. Scattering may be countered `~ 4 by use of filters in the remote sensing means that tend to passl S light that has not been scattered and to block light that has ¦
6 been scattered, or by using a remote sensing means that operates 7 at the millimeter and centimeter wavelengths (microwaves) that 8 ¦ can pass through fog and clouds with a minimum of attenuation.l 9 ¦ It is recognized that when the spectra no longer 10 ¦ reflect (spectra longer than 2.5 micro-meters) that the 11 ! telemetry must measure radiation in lieu of reflection.
12 ¦ (See Fig. 3.) It i5 believed that the radiation amplitudes 13 increased linearly by increased wave lengths will exhibit 14 phenomena similar to the reflective irradiance amplitudes. I
Combinations of simultaneous telemetry for reflective irradianle 16 and radiation may be mutually advantageous for remote sensing 17 because the null point is a common and natural index where 18 refl~ctance ends and radiation begins. For example, two 19 remote sensing means of this invention may be employed operating at different frequency bands to gather data about a 21 target surfaee and then the separate results compared. Thus, 22 both reflective and emissive spectra can be simultaneously 23 measured by two separate remote sensing means to gather 24 data in the full range of the electromagnetic spectrum.
As indicated previously herein, different wave 26 length bands can be employed in conjunction with the 27 I remote sensing means according to this invention. The 28 11 visible portion of the electromagnetic spectrum extends from 29 11 . 4 to 0.7 micrometers. The portion 0.3 to 15 micrometers is 30 '' the optical wavelength portion. Wave lengths shorter than 1~3~603 ~ Kouns-l . .
,.,, I . I
¦ 0.4 micrometers lie in the ultra violet region. Above 2 the visible spectrum lies the infrared region; 0.7 to about 3 3 micrometers is called the reflective infrared region; and th~
4 region from 3 to 15 micrometers is called the emissive or thermal infrared region. Instead of energy being reflected 6 ¦ in this latter region, it is emitted due to thermal 7 activity or heat.
8 The null point reflection and radiation is a 9 natural index point (See Fig. 3) for remote sensing with multispectral telemetry of targets. On the earth's ~ -11 surface, it could be significant when plotted with the 12 agonic lines. Composite reflection-radiation telemetry, 13 which includes spectral bands at and beyond the null 14 point in decreasing and increasing wavelengths respectively, lS and used by applicant's method, will not only improve remote 16 sensing, but also will identify options for information 17 extraction of data already archived by rotation of axes 18 and other empirical devices or algorithms using computers. -19 ¦ The intrinsic amplitude of irradiance for each spectrum is a discrete value composed of an integration 21 of a harmonic and stochastic process in which synchronous 22 limits are used instead of fixed limits. I~ is apparent 23 that spectra should be chosen in pairs such that the 24 ratios of their intrinsic amplitudes of irradiance (I~n~ arP proportional in pairs with equal slopes 26 but with different magnitudes.
27 It should also be appreciated that the 28 apparatus has been described in a relatively simple 29 !I form and that more complex apparatus could be utiliæed 0ll to increase the efficiency,. for example, by using " , , , v 11306(33 Kouns~

1 ~ multiple photopolarimeters and/or automatically ; 2Ij rotating the photopolarimeters to the desired angles.
3l, It will be understood therefore that such refinements 4¦1 together with automatic recording equipment and other 5 l¦ known techniques could be utilized to increase the speed 6 ll and efficiency of the apparatus disclosed and are within 7l I the scope of the invention.
i . I
8 ll The following examples illustrate a preferred 9 I embodiment of the method of this invention.
11 ll Example 1 12 ~ Two obstacles have sidetracked polarimetry.
13 ¦ Polarization is known to affect all light from its 14 ¦ sources through its recording. For remote sensing, this lS ¦, raises the problem o~ negating the optical thickness 16 ll between the light source and the target. This problem 17 applies to passive application with the sun or to active 18 application with a controlled light source. No polarimeter 19 has been developed for broad picture imaging. This example illustrates that digital interference spectroscopy 21 of precisely registered polarization data o~ point-to-22 point traverses on well-known ground surfaces can be 23 manipulated in computers to enhance discrimination or 24 signature differences. Also, it illustrates that the 25 ¦ traverses can be spaced to synthesize a mosaic or aerial 26 ¦ coverage ~or targets of interest and that the optical 27 I thickness between the target and the polarimeter can be 28 1' evaluated by comparing close, intermediate and long-29 range viewing o identical targets with temporal studies.
A polarimeter, the "visi,le Light Polarimeter . . 1130603.
Kouns-l I -1 ~ Lab. Type S046" (commercially available from General 2 Electric Company Space Division, PØ Box 8555, Philadelphia, ¦ -3 Pennsylvania 19101) was fitted with and calibrated to record polarization by Stokes parameters in four wave bands: ~n=0.5-0.6 microns; ~n~l0.6-0.7 microns; L
6 ~ =0.7-0.8 microns; and ~ ~-0.8-1.1 microns. The 7l polarimeter was used in conjunction with two interchangeable, 8 ¦I portable surveyorls tripods with cross-leveling. The 9 1I polarimeter was mounted on the other tripod during traverses 10ll of targets. The two tripods provided precise registration 11l of the polarimeter during traverses at about eye level.
12 ll The polarimeter was made portable by employing two inter- -:
131 changeable po~table power packs with a five hour capacity -14 ¦ and fitted for recharge and connections on standard llOV-60 cycle service. The engineering transit style .
16 configuration of tripod was motmted with precision controls 17 for orientation, azimuth and elevation. The surveying 18 configuration was needed to track th~ sun in elevation 19 and azimuth for the purpose of exploiting passively the solar flux and documenting the look angle or each target. s 21 The field of view of the polarimeter is depen-22 dent on its distance from a target. At twenty feet 23 distance, its field of view subtends a circle of one 4 foot diameter. At ten feet, it& field subtends distance, a circle of one-half foot diameter. At thirty feet, 26 its field subtends a circle of one and one-half fe~t 27 diameter. No picture image is formed within the target 28 ¦ circle as in photography. The data that are recorded 29 1 1 are the polarization intensities of the target surface.

30 ~ Since polarization has an intrinsic resolving power -.

Kouns~ 30603 ~1 !
1~ much more delicate than available in the usual lens 2 I systems, the correlation of surface truth with these 3 data provides an improved method of remote identifica-4 tion of targets.
5' The polarimeter itself had a cylindrical case 6l¦ about 5 inches in diameter and 16 inches in length.
7 ¦I The case had 5 barrels drilled coaxially with its 8 1 longitudinal axis. Two of these barrels were fitted with g~I dessicants to eliminate the formation of moisture on -101¦ the optical elements fitted into the remaining three 11~ barrels. Two polarizing prisms specifically cut from I -12 calcite crystals were mounted in adjacent barrels, with 13ll their directions set perpendicular to each other, along 14l a common fixed plane. The two polarizing prisms acted as filters to pass only the vertical and horiæontal 16 components of plane polarized light reflected by each :
17 target surface. These barrels were labeled B and D.
18 Between these barrels with the prisms and in the same 19 common plane (perpendicular to the longitudinal axis of the case) were apertures which pass light flux being 21 reflected by the target surface. This barrel was labeled 23 To the rear of the fixed B-D-I plane, there 24 was fitted a parallel rotating plane with four spectral filters on a common arc in the four wave bands previously 26 described herein. These filters passed the vertical 27 and horizontal components of polarized reflectance from 28 l the target simultaneously for their respective wave 29 l bands concur-rently with the unfiltered flow of the 30 1l light ~lux reflected from the target. The timing was ,, .

ns~

geared to a Geneva Movement so that one complete pulse 2 1l of all four bands was cycled in 1.3 seconds. This 3 I provided a code print-out of Q,U and ~ (I) for each of 4 the four spectral bands, ~ through~n~ respectively. Q, U and I are, of course, the Stokes Parameters for 61 polarized ligh~. They were converted to percent polarization 7 intensity (%PI) by solving the following quadratic 8 I equation for each of the four spectral bands: ¦ -9 ~ PI = 100 10 I The polarimeter was fitted to-a biaxial yoke ¦~l with a transit style mounting as previously indicated j herein to facilitate precise orientation and registration 3 1 of traverses by latitude and longitude. In addition, the case of the polarimeter was fitted with a gun 16 sight telescope for manual tracking of the sun or other ¦
17 targets. The polarimeter was also linked by a cable 18 to a central control panel and electronics package powered 19 by a portable battery unit with an AC inverter and a constant voltage device. The control panel was 21 linked by cable to a recorder that printed out the 22 Stokes Parameters cyclically in twelve coded line 23 pulses by band sequence, ~n through~n~3 24 A target surface situated at Bolling Dome, Newgulf, Texas was selected for a traverse with the 26 polarimeter. The mounting tripod was surveyed in at 27 the desired centerpoint of the traverse using map 28l ¦ coordinates of this area and a compass. The polarimeter, 29 ~ in its biaxial yoke, was set on the tripod so that align-3~ !l ment pins on the yoke mated with holes on the tripod ~ ! , ' . .

Kouns- ~ 1130603 11l head. A screw clamp was used to lock the yoke to the 2 !I tripod. Scales on the horizontal and vertical axes of 31 the yoke were used to record angular positions of the 4 polarimeter. A gun-sight telescope, as previously mentioned, was fitted to the polarimeter to facilitate 6 accurate aim at targets. Jack and plug fittings were 7 employed to ensure. proper linkage of the power unit, 3 I control panel, recorder and polarimeter.
9 The movement of the sun was manually tracked 10 I with the telescope. Measurements were taken and 11 ¦ recorded at ~ hour in~ervals. A few seconds prior to 12 j recording, the polarimeter was lowered below a horizontal 13ll orienta~ion to intercept the surface target at an angle 14¦ equal to the elevation angle of the sun. Print outs 15¦ were made using the polarimeter~ apparatus for about 6 16 seconds so as to obtain 4 complete sets of data.
17 The polarimeter was set up on the top of a 18 man-made vat of native sulfur stock-piled fifty feet above 19 the ground by the Frasch process of minLng. Readings of a selected target surface of the vat were taken 21 according to the procedure outlined hereinabove. The 22 two sharter wave bands ~n,~ht~had equal polarization 23 intensities while the two longer wave bands ~ ,~ also 24 had equal polarization intensities but of a different magnitude than the shorter pair, ~ ,~" .
26¦ The polarimeter was displaced 150 feet due 271 west of its original location on the vat to test 28 ! afternoon data on the vat-ground interface. Data 29 ~ readings, using the procedure outlined hereinabove, 30 l when the polarimeter was aimed at this interface, , ~ .

3L~L3~)603 ouns- 1 indicated the interface was heterogeneous as expected 2 1l since all four spectral bands provided unequal readings.
3 ! However, as the polarimeter was aimed at target surfaces 4 more distant from the vat, the conjugate pair phenomena reappeared indicating thehomogeneity of the target 6 I surface. The data indicating thishomogeneity are set 7 1ll forth in Table I hereinbelow:

~2 19 ~

1~3(~6~3 Koun~

_ 8 l o ~c ~ ~
9 lo ~ ' c c c ___ __ _ 10~ ._ _ c _ 11 . ~o~ , C~ ~ ~ o~ U~
13~ ~o--c c _~ .
.` 15~o-- _ _--.
, ` C`J _ _ 16 H O C C C C , 17 ~ ~ o o o o :
18 i~i o c _ _ c ` 1~ ~ _ _ .
o a~ oo c~ ~
_ _ 21 o ~ ~ ~ o _ _ 22o uol ~1 c o 23~o . . .
24. _ _ _.
25o o c c o 26 c~
27o o o 28 l~ u~ o o o o ! ~ ~ ¢
29 I ~ E~ o tY u~ ~o ,~
~4 ~ ¢ H E-~ . . .
. O ~ E~ E-l ~ oo o o 3 o I E-l ~¢ H ~ 11 11 D ll ,,, v~ ~0 1~
P~

~-Kouns-l 1 ¦I The polarimeter was displaced 20 feet 2 ¦ I due east of its original location on top of the 3 vat. Readings were taken for the following target 4 surfaces: an adjacent cow pasture, the sulfur vat, a sulfur surface about 55 feet below the polarimeter 6 on the vat and the ground-vat interface. The conjugate 7 pair phenomena was observed from the first three target 8 surfaces but not for the interface, thus revealing the 9 ¦ homogenity of the target surfaces by remote sensing 10 1 means. Moreover, the PII of the cow pasture was different 11 ¦ from the PII of the sulfur surface and the sulfur vat 12 ¦ targets each had substantially identical PII values.
13 ¦ Example 2 14 The procedure of Example 1 was repeated except that the polarimeter was set up on a platform 24 feet 16 above the ground on the top of an oil storage tank in 17 a pasture. Again when readings were taken using the 18 polarimeter on a target consisting of the pas~ure, the 19 conjugate pair of wave bands phenomena was indicated.
Also, the readings of the PII for the target pasture -21 was substantially identical to that of the PII reading 22 taken for the same cow pasture at a different distance 23 therefrom in example 1.
24 When readings were taken using as the target surface a road surface metalled wi~h pebbles in a 26 tarlike matrix, four unequal polari2ation intensities 27 were measured, indicating a heterogeneous target surface.
28 1¦ Example 3 29 1l Using the procedure described in Example 1, 30 11 a stone quarry situated near Centreville Virginia was ~L3{3603 Kouns-l 1 ¦ identified according to applicant's method. The east 2 11 and west walls of the stone quarry had near-vertical 3 faces of exposed rock. With the afternoon sun, the in- ¦
4 strument was surveyed in near the east quarry wall.
With a morning sun, the instrument was surveyed in near ; 6 the west quarry wall. The sun was then tracked manually 7 with the aid of the telescope. After ~ hour intervals, 8 ¦ without changing the tracking elevation, the polarimeter 9 I was rotated on its vertical axis in aximuth to intersect the closer quarry wall from which it received solar 11 flux reflected from the quarry wall at about the same 12 angle as the incident sunlight.
13 The track of the polarimeter readings was 14 vertically downward on the east wall and vertically upward on the west wall. A pattern of percent polarization 16 intensity evolved in conjugate pairs of wave lengths for 17 homogeneous target surfaces. However, it differed from 18 patterns for the generally horizontal target surfaces 19 with ~ " , and ~h~airing and ~ and ~ ~airing. Since the more horizontal suraces had ~ and~n~lpairing and ~tan~
21 ~ t3pairing as conjugate pairs, the regrouping was 22 attributed to the vector translational speed of the sun source 23 in a vertical plane versus vector translational speed of the 24 sun-source in a horizontal plane. The data gathered in this experiment during the traverse of the vertical 26 west wall of the quarry are reproduced below in 27 Table II: !

Kouns~

9 ~,~
14 ~ I ~ o~

16 ~ _ o c o .
17¢ _ _ _ _ .
18E~ _ o c o c o 19o u 1~ c o ~
~

23' -~o =- _ -. .

25o o o o o 26o c o o o .

28~ ~ ~ ~ o .
29 lu~ ~3 l . ~ E~ O ~~ r~ o~
30 ¦ o !~ ~ H ~ O Q ~ C; O
i E-~ ~ ¢ H W 11U 11 ll :' ' . ' U~ ~0 P~ .

'' '' ~Ll3HU6 ~3 Kouns~
,' 1 The significance of this grouping of 2 conjugate pairs differing for vertical surfaces makes 3 possible the exploration of wells and canyons by 4 polarimetry with controlled illumination sources.
Also, controlled light sources can be tailored to range 6 and navigate on selected signature isopleths of surfaces 7 for mineral exploration and the like.
8 In addition to all the previously suggested 9 modifications and variations, other variations will be apparent to those of ordinary skill in the art and it 11 is accordingly desired that the scope of the invention 12 not be limited to those embodiments disclosed nor to 13 the several variations and modifications suggested ¦ -4 but that the scope of the invention be limited only by 15 ~ the apper ed claios.

2~ .
:~- 21 .
22 .

24 .

~9 I . I

Claims (5)

WHAT I CLAIMED IS:

1. A non-contact method for remote sensing of the homogeneity of a substantially horizontal unidentified target surface comprising:
electro-optically detecting a train of optical waves reflected from said target surface with a photopolarimeter;
calculating the polarization intensities (PI's) of said detected optical wavelengths in four preselected spectral wave bands,.lambda.n, through .lambda.n+3, wherein 0.5 <.lambda.n? 0.6 micrometers, 0.6 <.lambda.n+1?
0.7 micrometers, 0.7<.lambda.n+2?.8 micrometers and 0.8 <.lambda.n+3?
1.1 micrometers;
calculating a polarization intensity index (PII) for said target surface by ratioing the difference between the PI of .lambda.n+2, .lambda.n+3 and the PI of .lambda.n, .lambda.n+1 with the sum of the PI of .lambda.n+2, .lambda.n+3 and the PI of .lambda.n, .lambda.n+1 provided that the PI of the four wave bands define two conjugate pairs .lambda.n, .lambda.n+1, and,.lambda.n+2, .lambda.n+3, each conjugate pair having the same PI, and the conjugate pairs .lambda.n, .lambda.n+1 and, .lambda.n+2, .lambda.n+3 being different from one another; and comparing the calculated PII for said target surface with PII values for predetermined target surfaces to identify said unidentified target surface.

2. A non-contact method for remote sensing of the homogeneity of a substantially vertical unidentified target surface comprising:
electro-optically detecting a train of optical waves reflected from said target surface with a photopolarimeter;

calculating the polarization intensities (PI's) of said detected optical wavelengths in four preselected spectral wave bands, .lambda.n, through.lambda.n+3, wherein 0.5<.lambda.n?0.6 micrometers, 0.6<.lambda.n+1?
0.7 micrometers, 0.7< .lambda.n+2?0.8 micrometers and 0.8<.lambda.n+3?
1.1 micrometers.
calculating a polarization intensity index (PII) for said target surface by ratioing the difference between the PI of .lambda.n, .lambda.n+3 and the PI of .lambda.n+1, .lambda.n+2 with the sum of the PI of .lambda.n, .lambda.n+3 and the PI of .lambda.n+1, .lambda.n+2, provided that the PI of the four wave bands define two conjugate pairs .lambda.n .lambda.n+3 and .lambda.n+1, .lambda.n+2 each conjugate pair having the same PI, and the conjugate pairs .lambda.n, .lambda.n+3 and .lambda.n+1, .lambda.n+2 being different from one another; and comparing the calculated PII for said target surface with PII values for predetermined target surfaces to identify said unidentified target surface.

3. A non-contact method for identifying a substantially horizontal unidentified target surface which comprises the steps of:
electro-optically receiving the polarized components of a train of electro-magnetic radiation reflected from said target surface;
electro-optically generating four first data signals representative of four first values corresponding to the Stoke's parameter Q, for four respective, preselected wave bands of said reflected radiation;
electro-optically generating four second data signals representative of four second values corresponding to the Stoke s parameter U, for said four respective, preselected wave bands of said reflected radiation;
electro-optically generating four data signals representative of four third values corresponding to the Stoke's parameter ?(I) for said four respective, preselected wave bands of reflected radiation;
electro-optically operating on the first, second, and third data signals for each respective wave band to compute a fourth, fifth, sixth and seventh data signal representative of the polarization intensity for said four respective wave bands;
electro-optically operating on said fifth and said sixth data signals to compute a difference between them;
electro-optically operating on said fifth and sixth signals to compute their sum;
electro-optically computing a ratio of said difference to said sum which ratio represents the polarization intensity index of said unidentified target surface;
comparing said polarization intensity index of said target surface with the polarization intensity indexes of previously determined surfaces to identify said target surface.

4. A non-contact method for identifying a substantially vertical unidentified target surface which comprises the steps of:
electro-optically receiving the polarized components of a train of electro-magnetic radiation reflected from said target surface;

electro-optically generating four first data signals representative of four first values corresponding to the Stoke's parameter Q, for four respective preselected wave bands of said reflected radiation;
electro-optically generating four second data signals representative of four second values corresponding to the Stoke's parameter U, for said four respective preselected wave bands of said reflected radiation;
electro-optically generating four third data signals representative of four third values corresponding to the Stoke's parameter ?(I) for said four respective, preselected wave bands of reflected radiation;
electro-optically operating on the first, second and third data signals for each respective wave band to compute a fourth, fifth, sixth and seventh data signal representative of the polarization intensity for said four respective wave bands;
electro-optically operating on said sixth and seventh data signals to compute a difference between them and their sum;
electro-optically computing a ratio of said difference to said sum which ratio represents the polarization intensity index of said unidentified target surface;
comparing said polarization intensity index of said target surface with the polarization intensity indexes of previously determined surfaces to identify said target surface.

5. A method as defined in claims 3 or 4 wherein said radiation comprises sunlight.