CN101251417B - Hemi-spherical instrument for measuring sky brightness - Google Patents

Abstract

The invention discloses a visible and near infrared wave band semispherical sky brightness measuring apparatus used in the daytime. Seven detectors assembled on a semispherical body convert skylight illumination values in various directions into electrical signals, and obtain the spatial distribution of sky brightness via the direct proportional relation between the brightness at the receiving surfaces of the detectors and the illumination and through the calibration of a radiance meter. The method of assembling the seven detectors fixedly on the support of the semispherical body according to vertical angles and azimuths is adopted to obtain the sky brightness values in various directions simultaneously and quickly, thereby not only monitoring the sky brightness in a certain direction in real time, but also monitoring the sky brightness in various directions simultaneously for easy study on the time and spatial distribution of the sky brightness. The apparatus makes up the defects of a traditional sky brightness measuring apparatus concerning measuring wave band, real-time property, portability, etc., thereby meeting the practical scientific research requirements in a better way.

Description

Hemi-spherical instrument for measuring sky brightness

Technical field

The present invention relates to the atmospheric optics field, specifically is a kind of instrument that reach near-infrared band sky brightness time and space distribution daytime as seen of measuring.

Background technology

When using the ground based device that aerial target is surveyed, atmosphere be can not ignore.It redistributes the part solar radiation energy, has formed the space distribution of endoatmosphere scattered light brightness, i.e. the notion of " sky brightness ".Along with the progress of detection means, this notion also extends to infrared even far infrared band by the initial visible light that refers in particular to already.On the one hand, in order to obtain the radiation information of aerial or extraterrestrial target, must deduct the influence of atmosphere.And when observing object, the luminance difference of object and background plays a decisive role.Therefore, understanding the sky brightness distribution is the first step of identification space target.On the other hand, sky brightness mainly is the result who is caused by air molecule and atmospheric aerosol particle diffusesolarradiation, and it has comprised the information of a large amount of constituent of atomsphere and state.To the research of this physical quantity will help further to understand atmosphere and with the interaction of radiation delivery.

Traditional sky brightness surveying instrument only works in visible light wave range mostly.Difference according to working method, can be divided into two classes substantially: a class is that specific sky is carried out image taking, WSI (Whole SkyImager) as U.S. Yankee company's T SI (Total Sky Imager) and California University development, they with half-sphere mirror with the image reflection of all-sky to being with on the fish-eye CCD, measure the Luminance Distribution of sky by the half-tone information of analyzing picture, this quasi-instrument can obtain the brightness value of sky all directions simultaneously, but the means of measuring brightness are comparatively indirect, and real-time not high (obtaining the time of all-sky image need more than 1 minute); Another kind of is to obtain Luminance Distribution with one or more radiation receiving trap scanning skies, as the equipment that uses in gondola WASBAM (Wide-Angle Sky Brightness Automatic Mapper) and the illuminating engineering, this quasi-instrument is to the sky discrete sampling, and structure is comparatively complicated, some needs mechanical rotation, causes measuring period longer.

Yet in actual applications, often wish to monitor in real time the variation of sky brightness, detecting band is extended to wider scope, realize the miniaturization of instrument and the simplification of structure simultaneously.Therefore, be necessary to develop a kind of instrument of new measurement sky brightness,, better meet actual scientific research demand to remedy traditional instrument in the deficiency of measuring aspects such as wave band, real-time.

Summary of the invention

The purpose of this invention is to provide a kind of hemi-spherical instrument for measuring sky brightness, measure by the time, the space distribution that are distributed in a plurality of detectors realization sky brightnesses on the semisphere support.

The technical scheme of patent of the present invention is as follows:

Hemi-spherical instrument for measuring sky brightness, it is characterized in that: include hemispheroidal detector carriage, seven grooves are set on hemisphere, a detector is installed in each groove, constitute seven and measure passage, detector radially is provided with by hemispheroidal, and test surface points into the sky, its position coordinates is (55 ° in a passage 0,198 °), passage 1 (30 °, 162 °), passage 2 (30 °, 54 °), (55 ° in passage 3,342 °), passage 4 zeniths, (30 ° in passage 5,270 °) and passage 6 (55 °, 126 °), first amount is elevation angle in the bracket, from the local horizon, upwards for just; Second amount is the position angle, from south gets, along clockwise, westwards for just; Each detector pin connects shielding line, and shielding line is drawn from the perforate on the described groove, receives data storage and treatment facility.

Described hemi-spherical instrument for measuring sky brightness is characterized in that: described detector adopts photodiode, the incident light of response 320nm-1000nm, and the linear work interval is 10 ^-6-10 ⁵Lx.

Described hemi-spherical instrument for measuring sky brightness is measured the method for sky brightness, it is characterized in that: with the detector carriage horizontal positioned, around guaranteeing elevation angle more than 30 ° clear block, detector is converted to electric signal with the illumination of a certain direction of sky; At zenith direction, think that the measured value of spoke nitometer is the actual value of sky brightness, demarcate detector on this direction with this, obtain the response function of this detector to sky brightness, promptly try to achieve the relation between sky brightness value and the detector voltage value; Under the approaching situation of all detector performances, think that they have identical response function, just can obtain the sky brightness value by the magnitude of voltage that all directions detect.

The present invention adopts photodiode as detector, and a plurality of detectors are placed on the semisphere support according to elevation angle, position angle, measures the sky brightness of different directions simultaneously, and response wave band is 320nm-1000nm.

Advantage of the present invention:

(1), detector wave spectrum scope is extended to near-infrared band from visible light, meet the true scope that solar energy distributes more, also more meet the reality of atmospheric optics research.

(2), in a short period of time (0.4 second) obtain the distribution of sky brightness, help studying the transient change that sky brightness distributes.

(3), both can monitor the sky brightness of a certain fixed-direction, also can monitor a plurality of directions simultaneously, make things convenient for the application in the reality.

(4), can obtain the absolute value of radiation, also provide a kind of new calibration means simultaneously for the type sky brightness surveying instrument of taking pictures.

(5), simple in structure, easy to carry.

Description of drawings

Fig. 1 is a system construction drawing of the present invention.

Fig. 2 is the synoptic diagram of semisphere support of the present invention.

Fig. 3 is a detector distribution schematic diagram of the present invention.

Fig. 4 is that detector of the present invention is placed synoptic diagram

Fig. 5 is the time variation diagram that the sky brightness that records of the present invention distributes

Embodiment

See also accompanying drawing 1.Photodiode is converted to electric current with the illumination of a certain direction of sky, through the high precision operating amplifier changing voltage, and with feedback resistance voltage is adjusted to required amplitude.Signal acquiring system is made up of 7 passages.During unsaturation, the brightness value of test surface is directly proportional with the brightness value of its detection direction, so the resulting magnitude of voltage of system can reflect the power of sky brightness.Calibration by the spoke nitometer obtains the response function of detector to brightness, under the approaching situation of all detector performances, just can be obtained the sky brightness value by the magnitude of voltage that all directions detect.

One, the requirement of spectral response range and signal linear response range two aspects is mainly considered in the selection of detector.The wave spectrum scope of sunshine is very wide, and energy distribution is all arranged in the wavelength coverage of 300～3000nm.But owing to do not respond so wide photo-detector of bands of a spectrum, so World Meteorological Organization (WMO) will concentrate the 400nm～1100nm wave band of most solar energies to be called the built-up radiation scope, and this this instrument spectral response range that should have just.In addition, instrument is to be used for measuring non-severe weather conditions sky brightness on following daytime, should be able to be 10～10 to intensity thereby require detector ⁵The light of lx produces linear response.Therefore, select the S1787-12 type photodiode of HAMAMATSU company, it can respond the incident light of 320nm-1000nm, and the linear work interval is 10 ⁶-10 ⁵Lx.

Two, the support of detector is a hemisphere, sees accompanying drawing 2, internal diameter 94mm, external diameter 110mm.Consider hardness and insulativity, adopt polytetrafluoroethylmaterial material.7 grooves 1 are arranged, to place detector 2 on it.Choose 7 (30 ° of 4 skies district (all directions) and 3 elevation angles, 55 °, 90 °) upward distribution is comparatively even, can represent the observed bearing of all-sky Luminance Distribution to place detector, according to astronomical custom, with Horizon coordinate representation is (30 ° in passage 0 (55 °, 198 °), passage 1 (30 °, 162 °), passage 2,54 °), (55 ° in passage 3,342 °), passage 4 zeniths, passage 5 (30 °, 270 °) and passage 6 (55 °, 126 °), as shown in Figure 3, first amount is for elevation angle in the bracket, from the local horizon, upwards for just; Second amount is the position angle, from south gets, along clockwise, westwards for just.

Three, the placement of detector 2 as shown in Figure 4.Leave seven grooves 1 on the hemisphere surface, with the test surface of detector up, what lie low puts into wherein, and each makes a call to a through hole below two pins, and shielding line respectively in the patchhole, is connected pin and subsequent conditioning circuit.Detector belongs to exact instrument, for guaranteeing the intact of its performance, lead can not be welded on the pin, but should be entangled on the pin, and fix with thermoplastic tube.

Four, the maximum sample frequency of capture card is very high, and sample frequency reasonably is set can load by mitigation system, reduces follow-up data processing amount.In the working environment of reality, the variation of sky brightness mainly is by natural cause, under the influence of not considering the atmospheric optics turbulent flow, mainly be by the sun on high the orientation and the variation of wind, cloud cause.For such low frequency signal, the sample frequency of every passage 2.5Hz is enough.

In host computer, show control by in VC++, adding image, 7 road signals can be simultaneously displayed on the screen, the operator has been had the variation of signal get information about.

Five, instrument is owing to relating to position angle, elevation angle, so need the placement of compass, level meter calibration instrument before use.Near instrument, be to have object to block in 30 ° of the elevation angles of initial point with the hemisphere centre of sphere.Be the confidence level of determining to measure, need before use detector is hidden, to measure ground unrest.

Six, measuring principle and method:

Brightness is the physical quantity of describing light-emitting area photometry characteristic.Its physical significance is that on a certain observed ray θ, from the radiation flux Φ that the projected area s of unit sends in unit solid angle Ω, brightness B is formulated as

$B=\frac{\mathrm{d\Φ}}{\mathrm{d\Φ}\mathrm{ds}\cos \mathrm{\θ}}$

(1)

For photodiode, in the scope of certain incident light level, output current I and incident light illumination E are linear:

I＝c ₁E+c ₂ (2)

Behind the current-voltage conversion circuit of forming by amplifier, the voltage V that measures:

V＝c ₃I+c ₄(3)

Consider that the received illumination of the sky brightness of its detection direction and test surface is directly proportional, promptly under the situation about determining in the geometry parameter and the position of photodiode

B∝E (4)

Comprehensively (2)-(4), the voltage V that detects of system becomes a simple linear relationship with sky brightness B as can be known:

B＝aV+b

(5)

Just can obtain sky brightness on this direction by the magnitude of voltage of measuring system on the sky all directions, and system responses parameter a, b can obtain by the calibration of a certain direction spoke nitometer.

Seven, model experiment result:

On November 6th, 2007, weather is fine with occasional clouds, and gentle breeze is measured the sky brightness result as shown in Figure 5.

Claims (3)

1. hemi-spherical instrument for measuring sky brightness, it is characterized in that: include hemispheroidal detector carriage, seven grooves are set on hemisphere, a detector is installed in each groove, constitute seven and measure passage, detector radially is provided with by hemispheroidal, and test surface points into the sky, its position coordinates is (55 ° in a passage 0,198 °), passage 1 (30 °, 162 °), passage 2 (30 °, 54 °), (55 ° in passage 3,342 °), passage 4 zeniths, (30 ° in passage 5,270 °) and passage 6 (55 °, 126 °), first amount is elevation angle in the bracket, from the local horizon, upwards for just; Second amount is the position angle, from south gets, along clockwise, westwards for just; Each detector pin connects shielding line, and shielding line is drawn from the perforate on the described groove, receives data storage and treatment facility.

2. hemi-spherical instrument for measuring sky brightness according to claim 1 is characterized in that: described detector adopts photodiode, the incident light of response 320nm-1000nm, and the linear work interval is 10 ^-6-10 ⁵Lx.

3. utilize the described hemi-spherical instrument for measuring sky brightness of claim 1 to measure the method for sky brightness, it is characterized in that: with the detector carriage horizontal positioned, around guaranteeing elevation angle more than 30 ° clear block, detector is converted to electric signal with the illumination of a certain direction of sky; At zenith direction, think that the measured value of spoke nitometer is the actual value of sky brightness, demarcate detector on this direction with this, obtain the response function of this detector to sky brightness, promptly try to achieve the relation between sky brightness value and the detector voltage value; Under the approaching situation of all detector performances, think that they have identical response function, just can obtain the sky brightness value by the magnitude of voltage that all directions detect.

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