CA1275313C - Photoelectric ice accumulation monitor using dual detectors - Google Patents

Abstract

ABSTRACT
Apparatus and method using internal reflection of electromagnetic radiation to detect ice or water on pavements or other surfaces and to continuously measure the thickness of the accumulation. A prism which is transparent to pulses of electromagnetic radiation from an emitter is mounted in the pavement with an exposed prism surface flush with, and in the plane of the surface being monitored for the accumulation.
Radiation from an emitter is directed at the exposed prism surface at an angle so that the radiation is totally reflected when the exposed surface is bare, but only partially reflected when there is an accumulation. Radiation detectors are positioned so that changes in the intensity of internally-reflected radiation are measured and interpreted to detect the onset of an accumulation, measure the thickness of the accumulation, distinguish accumulations of ice from accumulations of water, and distinguish accumulations of mud or dirt from accumulate ions of ice or water.

Description

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2 ¦ There are many place~ where ins~all~tion of ice accumulation 3 ¦ monito~6 could be advan~geou~O ~y way of example:

4 ¦ At a1rports~ operationR personnel could use 1nformation fzom 5 ¦ ice accumulatlon monltor6 to ~lert ~hem to un6afe operatlng 6 ¦ condltions cau3ed by lce ac¢umulation on runway~;

7 ¦ On highways~ in~ormation ~rom lce accumulation monito~s 8 ¦ could actuate 8ign~ to alert motori~t6 of dangProus icings, and 9 ¦ inormation rom ice accumulation monitor~ could inform highway 10 ¦ department per~onnel a~ to where tbe highway~ nePd sanding, 11 ¦ salting, and/or ice removal;

12 ¦ On buildings, ice accumulat~on on roof~ could be monltored 13 ¦ to indlcate when ice r~moval wa needed~

14 ¦ On aircraf~ wings and o~her aircraft s~rface~, ice 15 ¦ accumulation monitors woul~ provide informat~on to warn aircraft 16 ¦ operators of unsafe ice buildups~ and 17 ¦ On radomes, ice accumula~ion monitor6 would activate deicing ~8 ¦ equipment when ice accumulation is great enough to interfere with ~9 ¦ reliabl~ operation of the enclosed antennas, or. warn per~onnel 2~ ¦ when deicing was necessaryO
21 ¦ ïn re~erenc~ to previously disclosed equipment used ~o 22 measure ice accumulations, there has been:
23 Equipment :~or me~suring ice accumulation by analyzlng c~any2~ tn ~recduency of an oscillating element as lce accumulate~
2~ on the elementO ~he ~l~men~ generally protrudes iErom a ~ur~ace~
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~, -1 ¦ 50 the element i5 susreptible to traff ic da~D2ge when ~nstalled in ~ ¦ a roadways Al~o becau~e the element protrude~ rom the surfa~e 3 b~ing monl ored, $cing conditions on the element may differ rom 4 icing conditions on the ~urace. In anc~ther embodiment of æuch 5 an osc~llating element, a protective cap~ flat for roadway~, 6 accumulate~ d ir~ ~o that this element i~ not rel:lable because it 7 does not dlstin~ui~h between dir'c accumulation and ice 8 accumulat ion;
9 EquiplDent or measuring ice accumula~ion by analyz~ng changes in the obstruction of light by the formation of ice, witb the light channel portions protruding above the ~urface and 12 thereby being subjç~ct to damage by traffic and inacc:uracies associated with protrudlng elementsi 14 Equipment for meaF~uring ice accumulation by analyzing 15 changes in the pressure drop across an orifice9 being caused by 16 the formation of ice, with orif ice por~ions protruding above the 17 surface and thereby being subject o damage by traffic and to 18 inaccuracies as~ociated with protruding elements~

19 ~quipment using internal reflections to detect ice formatior on a ~urface, a~ set fortb in U.S. ~aten~ 2~359,78~. HoweYe~a 21 this equipment does not measl re ~he amoun~ o~ ice accumulated) 22 and does not indicate methods for compensatlrlg for interferences 23 ~rom chang~s in ambient light o~ ~or di~tinguishing the pre~ent::e 24 o~ dir~ or mud~ and Equipment using internal reflecl:ions to d~tect ~ce formation ' .

--~ 3~3 ~ 1 on a surface,1 as set forth in U.S. Pa~ent 3,540~02~. ~owever, 2 this equ ipmen~ u~es a se~ ies of hea'cin~3 steps followed by removal 3 of the melted ice, to indlca~e ice formationO Because the~e 4 meltlng steps interfere with ice accumulations, continuou~
5 mea6uremerlt~ of ic~ accumulatlon are not pra¢~ical with ~his 6 e qu ipmen t ,, 7 The prior equipment is believed not to have been adequate in ~ measurlng accumulationG of lce and espec:ially inadequate for 9 measur ing the continuisus accumulation of cracked or otherwise f lawed ice .
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13 This ic:e accumulation monitor ~dequately mea~ure~ ~.he 14 accumulation o ice, includ~ng accumulations o cracked, or o~herwise ~lawed ice, as i~ ocs::urs on any ~urface, such as 16 roadwaysD airport runways, sidPwalks9 radomes, aircraf~ sur~acesJ
17 and the roof~ o buildings. The ic~ accumulation mon tor 18 inc:lude~ a prism which is transparent to radiation emitted by an 19 emitt~rg which prism ha~ one surface exposed to~ice accumulation, thls surace being flush with, and cont nuously in the same plane 21 as r the surface be~ng monitored; an emitter o~ pul~ed 22 electromagnetic radiatioll orlerl~ed so ~hat a~ ~che exposed prism 23 surface the emitted radiatiorl is ~otally rel~ected within the 2~ prism when the exposed sur~ace ~s ~are, but the emitted radiation ~s only parit{~lly reflected within the pri~m w}~en ice cover~ the __ ._ _ . . . ... . ..
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~ ~-t 3 1 exposed prism surf~ce; and ~wo radiation detectors to measure the ~ lntensities of the reflected radiation, and located with one 3 detector clo~er to the e~posed surface than the other detectorO
d~ A temperatur0 sensor, located ln the pr ism near the exposed 5 surface; i8 used to aid in distinguish:ing accumulations of ice 7 from accumulations of watera Preferably th~ expo~ed surface of the prism is al80 a surface of a very hard transparent layer that 8 will not be ~cratched or otherwlse d2maged by traff ic or o9:h~r 9 abusive elements. To avoid nonl~near detector responses at the 10 relatively high radia ion levels that can result from ome 11 ambient ligh lng conditlorls, a bandpass filter, with its bandpass 12 wavelength centered near the dominant wavelength emitted by the 13 emitter, is located at a position in the prism that s:~au es the 14 amount of ambient radiation reaching the detector6 to be reducedO
15 The effect of ambient radiation lz then eliminated from the ice 16 accumulation measurements by subtracting the rad iation detector 17 responses when the emitter is in the off portion of its cycle 18 from the rad iation detectos responses when the emittPr is in he 19 on portion of its cycle.

20 ¦ When ice is not present on the exposed surface of the pxism"

21 ¦ the emitted radiation is cc>mplete}y reflected back into the prism 22 ¦ at the expo~ed prism surfacl3 and detected ~y the ~adiation 23 ¦ detectorsO ~he relative position~ of the d~Ptect~rs.i~ ~ucb that 24 ¦ the intenf;~ty of rad~ation detected by one de~ector is greater 2~; than detecteà by tbe other detector. When ~c:e ~tart~ to .

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~ 3~3 1 accumulate, some of the emitted radiation is transmitted into the 2 ice~ thereby reducing ~he amount of r~dia~ion reflected ak the 3 exposed surfac~ Tbis reduction in radiation reflec~ed at the 4 e~posed surface, combi~ed with the dif~erent path to the detector~ by radiation re~lect~d at ~he ice-alr interface, 6 changes the radiation i~tenæitles detecSed by each det~ctorO
7 Through calibration, ~hese changed intensities are relat~d ~o ~he 8 amount of ice accumulated~ By this method, accumulation~ sf 9 cracked, or otherwise flawed, lce, as well a6 accumulation~ of la pe~fect ice can be detected and measuredO
11 In callbra~ing this ice accumula~ion monitor, ~he dominan~
12 wavelength o~ tbe emitted radiation is selected ~o that ~he inde~
13 of refractlon of ice at ~his wavelength i~ practically ~he ~ame 14 as the index of refrac~ion of water at this wavelength~ ~ereby allowing accumulations o~ water to be u~ed to determ~ne a 16 callbration ~urve for each radlation detector. Additional 17 calibrations are undertaken o the ~ea~ured intensities of the 18 reflected radiation will indicate when the e~posed surface of the 19 pr i8m i~ cover~d with dirt or mud and needs cleaning.
As so arranged D installed, and used, this ice accumulation 21 monitor adequately m~a~ures the accumulation of ice in all of it~
22 formationsO If dirt or mud appear, their presence is detected, 23 ao they may b~ removed and ~he measurement~ can he resumed~ The 24 meaaurements ~ay be tran~mitt~d to central observing instruments, to nearby ~igns~ a~d to other place~ to warn inter sted observe~g .~' ' ~ .

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~ of tbe amount of ice accumulated on the monitored ~urface,.

4 The lce acc:umulat~on monitor i~ ~bown" in ~eference to a preferred embodlment, in the drawings~ whereins 6 Figura 1 shows tbe reflectivity of bared and ice ~overed,, 7 fu6ed quartz 1nterfaces ~or unpolarized radiation orig:lnat~ng in 8 the fused quartz;
~ Figure 2 i~ a vi~3w of the ice accumulatlorl monitor in th~
10 pl2ne of a ~urface l:hat 15 ~eing monitored fo~ ice accumulat~on;
11 Figure 3 i8 a schematic sec~cion view of the il~e ac:cumulation 12 monitox pv8 itioned s~lth ~he exposed surfaoe ~f it~ transparent 13 prl~m flush withp and contiruou~ withr the surfac~ being 14 monltored or ice acc-lmu~ation" and $ndic:ating the location oiE an 15 emitter of pul~ed electromagnetic radiation, the locat~on~ of 'cwo 16 radia~cion detector~, the location of a len~ for collimating 17 radiation from the emltter, the location of a bandpas~ fill:er 18 positioned 1:o reduce the amount of ambient radiation reaching th 19 radiation detectors~ and a locatior; for a . empera~ure sen~or~
Figure 4 i8 a s hemat ~ diagram of an emitter drilveJc:ontrol 21 circuit ~or temperature-independen~ pul~;ed emis;lon from a laser 22 diode/photodiode package~
23 Figure 5 is a ~c~ema ic d~agram of an emi~'cer drive,~c:o2ltrol 2~ circuit ~hat u~;es a thermistor as a ¢ontrol element to obtain 25 temperature-ind~pend~n~ pul~ed emi~;ion frsm an emitter that doe~

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9.~ 3 -1 not bave an in~egral means for monitoring eml~sion in ensity~
2 Figure 6 i6 a ~chematic: 6ection view, showlng an optlcal 3 fiber ~or transm~tt:lng emitted radiation from a remote emittez ~o 4 the prism~ and 6howing optical fibers for tran~mitting internally reflected rad~ation to remote detectors~
6 Flgure 7A shows an alternative ~ rectangular prism c~o~
7 section, with the emiltter and de~ec:tor located within the prlsm;
8 Figure 7E~ shows an alterna'cive, ~riangular prism cro~s 9 ~ection, with the emikter~ and detector located on pri6m urfac:e~;
lo Figure 8 i~ a schematic sectiona~ view, imllar to figure 3, 11 but showing electr~cal connection6 to a cablLe connector ~ and the 12 prism in a container and cushi~>ned ~y an elastic material~
13 Figur~ 9 show~ a ~chematic c~rcuit diagram of a s:on~tant~
14 current 80urc~ driving a thermi~tor temperature ~en~or;
Fi~ure lû is a schemstlc sectional vlew" similar to igure l~i 3, but showing an accumulation of ice on the surface bei~g 17 monitored and on the expo~ed surface of the transparent prism, 1~ and showing a path for emitted radiation that is reflec:ted from 19 the eacposed surface of the prism and a path for emitted radiaition 20 that is re~lected iErom the ice-air inter~ace of the accumulated 21 ice, 22 Figure ll shows rad iation detector responses to 23 accumulal:lons of p~riEect ice or of water, and ~hows ranges of ~ respon~e& to an accumulation o~ flawed ice;
Figure 12 shows an interpretat~on of radiation detector ~ ~753~3 1 ¦ re6pon~e~ a~ bands of accumulations;
2 ¦ Flgure 13 ~;hows detect~r responseE; corre~pondirlg to ps~ ble 3 ¦ accumulat$o~ of water ~ and 4 ¦ Figures 14a and 14b show logical steps involved in analyzing 5 ¦ data ~rom th~ radiation detectors to eliminate the effect of ambient 6 ¦ radiation, to discriminate against accumulation of water, to 8 ¦ discri~inate against deposits of soil ox o~ mud, to determine ice 9 ¦ accumulatiorls, and/or warn of dangerous ice accumulations.
'lU i ~_~ _ l To provlde a backgro~.and for understanding ~he equipment and 12 ¦ opera~ion de~cribed, opticE; concepts that relate to thi~ lce 13 accumulation monitor are described ir to then the equipm~n~ and i~ operatiLon are describeda ~hen a light wave (electromagnetic radiation~ i~ incident a'c 16 an interface between two tran~;parent ~aterials with different 1~7 indexe~ of refraction" the wave ~;plits into t~o waves; a 18 transmitted wave which proceed~ into ~he sec~nd materi3.1f and a 19 I reflect~d wave which i~ propayated bac:k in'co-~he fir. t matelials, 20 ¦ Snell'6 Law relates th~ or~en ation of khe r~diation ~chat i~
21 ¦ transmi~ed into ~he second material ~o the orientation o the 22 ¦ inc iden t r ad iat ion ., 23 I The proportion of the inciden. energy that is reflected at I the interface 15 characterized by the reflectiv~ty (t~e energy æs I a~3socia~eed w~th ~he reflected wave divided by ~he en~rgy . ' , . . .
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` 1 as~ocia~ed wlth the incident wave) which can be calculated froin ~ Fre~nel's formulas~, and which depends on the angle of incidence, 3 ,0~, ~the angle that ~he incident wave alakes wlth the normal to d~ the interface~ ~ and which also depend~ on the ra'cio oiE the inde2~e~ o refrac~loll of 'che ma~er ial~ on either ~;ide s;~f th~
6 interface. A xeflectivl~y of one indic:ate~ total reflec'c~on~, 7 Figure 1 shows the reflectivi~y of bare 12 and ice-cs~7ered 8 13 fused quartz interface~ iEor unpolar:Lzed radiatls~n originatlng in the fused sIuartz. For lncident angles greater than a critical angle7 ~c~ described by 11 0c ~ (n~nl~ ~ n2~
12 where nl i~ the inde~ of refrac:tion of the material ln which the 13 radlation originate~ and n2 is the lndea~ of refrac~ion o~ the 14 ma erial on the other 8ide of the interface~ the reflectiYity iB
one and the incidlent radiation is totally reflected. For 16 inc~dent angles less than the critical angle, the reflectivity ~
17 less than one, 80 some xadiation i5 transmi~ted acro~ the 18 interface into the material on the other slde of the lnterface.
19 The critical angle for bare fu~ed quartz is 43, and for ice-covered ~u~ed quaxtz, the cri~ical angle is 64. Therefore~ when 21 ~ce cover~ a fu~d quar~z 8urface and radiation is incident at 22 the inte~face at an angle le~ than 64~ only part o~ tbe 23 incident rad~tion will be reflected~ the balance will be 2~ ~c ansmitted lnto the icea In ad~ition, ~nell'~ Law, ~ombined with ~quation 1~ show~ that the radia~ion that i~ tran~mi~t d I ~ ~
I ~ 3~3 ~ into the ice will be totally reflec~ed a~ 'che ~ubsequant ice-air 2 interface if the radiatlon inc~dent at the fused quartz interface 3 is incident a~c an angle greater than the critical angle for the 4 bare fused quartz interface ~43) 9 and the fu~ed guartz-air and S ice-air interfaces are parallel. Therefore,, ~adiation that i8 6 ~nc ident at an ice covered used quartz interfac:e at incident 7 angles between 43 and 64 will be parkially reflected ait tbe 8 interface and part~ally tran~mitted into the ice~ with that I?art that i~ transmitted lnto the ice being totally reflected at the 10 ~ubsequent ice-air interface.
11 In figure 2~ th expo~ed surface 14 of the prlsm 17 of an 12 ice accumulation monitor 15 that use~ these optics conc~pts is 13 shown surrounded by a surac:e 16 that i6 to be monitored for lce 14 accumulationO E'igure 3 show~ a cross s~ction of the pri~m 17 15 . with a rad lation emitter 18, and a detector lg comp~l~ed of 16 separate radiation detectors 20 and 21, arrangad to u~e these 17 optics concepts to measure ice accumulation on the surface 160 1~ ~h~L~
19 In the preferl:ed embodimen~, the emi~te~ 18 is a 20 ¦ commercially ava~ lable la~er diode/photodlo~e package in which 21 ¦ the p~otodiode monltors ~he emission inten~ity o~ the lase~
22 ¦ diode, 60 that outpu~ from ~h~ photodiode can be used as feedbacllc 23 ¦ irl an electronic circuit to laaintain ~che la~er diode emis~ion intensi~cy constant regardles~ o~ tempF~ratureO Emitter opera~ion is also pulsed, so that the e~fect~ of cbange. in ambient ~O

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1 rad~ation can be elimlnated from ice accumulation monitor 2 operation 0 By way of example, f igure 4 6hows a method for 3 electronically controlling ~he emltter 13 to obtain Pmperatllre-4 independent emi~s~on intan~lty 30, and to obtain pulsed 5 operation,. 0UtPU~ from the photodiode 31 i~ the laser 6 d iode/pho~od iode pac:kage i8 used as ~eedback to cont~ol an 7 operational amplifier circul~ 32~ which supplies khe laser diode 8 drive current,. Pul~ed em~tter operation ls obtained by using a 9 pulse generator circui~: 34, based on a timer integrated circuit~
10 ts~ provide a ~quare wave input 35 to the operational ampll ier circuit 3~ and to the amplifier section 336.
12 Alternatively~, ~n emitter such as a laser dlode or a light 13 emttt~ng diode ~LED) that does not contain an integral emission 14 moniltor can be u~ed with feedback from a temperature sensor 22 to 15 ob~air~ t~mperature~ dependent emis6~0n., Temperature sensor~
16 usable for this purpose include thermocouples, resistance 17 temperature de~ec~ors (P~lrDs) ~ solid state temperature devices~
18 and thermistor~; 9 By way of example, f igure 5 ~hows a method for 19 elec:tronically controlling opera~ion of a LE~ emitter 36 to 20 obtain a corlstant emisslon iIlten~ity 30 regardless of teDIperatu~e 21 and tD obtain pulsed emissions., ~n operational amplifier c:ircuit 22 37 dri~eR an amplifier section 32~, which supplies the I-ED drive 23 curren. Temperature depen~len~ feedback to the op~rat~onal 24 ampl;f ier ts provided by a thermis~oE 22 so tha~ ~he outpu~ o~
25 the operational ampli~ier changes to offset changes in emis&is:~

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1 ¦ lntensi~ty tha~ would re~ul~ from temperature change~. Output 2 ¦ from the operational amplif ~er i~ proportional to the thermi~tor 3 ¦ resl~tance, which ls proportional to temperature, ~o me~urement 4 ¦ s~f ~che operatlonal amplif ier OU~pll~ voltage, TEMP O ~180 provide~
5 ¦ a means for mea~uring the ~emperature, which will be uæ~d in 6 di~tingui~hlng lce accumulation~ from accumulation6 s~f water,.
7 As ~hown in f igures 3 0 8, and lO O ~he emitter 18 i~ mounted 8 withln the prl~m 17 and oriented ~o 'chat when the em~tted 9 radlation reache~ the expo~ed ~urface 14, it i~ in~ident at an angle greater than the critical angle for a bare e~po~ed surface, :11 ~0cYbare' but le~s than the crltical angle for an ice-covered 12 exp o~ ed s u r f ace ~ 0c ~ ic e-c ove r ed c 13 Alterna~ively thi lce accumulation monitor will operate 14 effectlvely with the emit~er mounted on the ~Loplng prism ~urface lS 26 and the emitted rad i ation d irected at the eYposed sur~ace 1~
16 60 that the radiation is incident at the e~posed ~urface 14 at an 17 angle greater than 0c~b~re but le~ than 0c~:~ce-covered' or thi 18 ice accumulation monitor will also operate effectively with the 19 emitter 18 e~erlor ~co the prism and the elsitted radia'cion 20 tran~mitted to the prism~, and directed a~c ~he expo~ied surface at 21 an incid~nt angle greater than 0c ~ba~e but le~s c ic:e 22 c~ve~ ed by an optlcal f iber 38, as shown in igure h . Therefore 23 it i~ under~tood that the efectivene~s o~ th~ ic2 accumulatlon 24 monitor i8 llOt limi1;ed tc> emit~er placement; within the prism.
In addit~on, thi~ ice accumulation moni~or 15 will al~o . 12 .

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~ 75;1: L3 1 ¦ operate a~ de~cribed hereaf~er under ~_ 2 ¦ Q~ i$ the emitter i8 or iented to produce less than total 3 ¦ reflec:tlon at the bare ea~poaed ~urface- ~owev~r, in thi~
4 ¦ situation, reflect$on at the lc:e-air interface i~ leas than total 5 ¦ and operation ls le~ efiEective, ~o emitter s~rientation producing 6 ¦ total reflec~lon at ~he bare expo};ed ~urfacP 1B preferred~
7 ¦ A lens 23 i~ located in a cylindris:~al cavity 24, which abut 8 ¦ the emitter 18, to be effective in c:ol:l imating the radlat~on from ¦ the emitter . Some emitter~ have int~3gral ::olllmating optlc:s 80 a 10 ¦ separate collimating lens 23 would not be requlred for the6e 11 ¦ emltter~ O Elowever ~ rad iation em~tted by many emiJcters is no~
12 ¦ ~uff iciently collimatad to provide e~fective operation of the lce 13 ¦ accumula~ion monitor, ~o the collimating len~ is lndicated in 14 ¦ this preferred embodiment~.
15 I ~h~i~m 16 ¦ The pr ism 17 is tran~parent to rad iation emitt~d by the 17 ¦ emitter 18 and ~n ~he preferred embodiment the prism ~ection 3-3 18 ¦ has a trapezoidal shape as ~;hown in figure 3. Elowever~ aB lo~g 19 ¦ as the ori~ntation of the ~mltted radiation ~ith respect to the 20 ¦ exposed sur~ace 14 i~ such that significant reflection 0C:611r~; at 21 ¦ both he bare e~posed surface and at the ice-air interface of an 22 ice-covere;9 exposed surface~ ~his ice accumulation monitor will 23 opera~ce eiEfec~ively wi~b prisms havin~ other ~:ro~æ sectional 24 ~hapes, ~uch a~ the rectangular ~;hape ~hown ln f igure 7A and the 25 triangular ~hape shown in ~igure 7B. There~ore it is under~ood .

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~ 5;3~3 1 that the ef~c~ivene~ o ~hi~ ic:e accumulation monitor is not 2 limited to prisms having the trapezoidal shape ~uch as 6hown in 3 ~Eigure 3.
4 In the pr~erred embodimerlt th~ p;t:i8m i5 made of fu~ed 5 quartz, but thi~; ~ce accumulation monitor will also operate 6 e~fectively with a p~$~m made ~rom any oth~r optical quality 8 material which i~ . ran~parerlt to radiation from the emitter and has an indeY of re~raction greater than the inde2~ of re~rac:tion of ice. One embodiment of the preferred emitter emit~ a'c 8~0 nm.
10 For this emitter, such other mater ials include most optical 11 glasses, ~apphire, and ruby.
12 The longer 14 of the two parallel ~urfaces of the prism is 13 e:~po~ed to lce accumulation ~ and i~ arranged flush with the 14 surfac~ 16 which is to be monitored for Ice accumulation.
15 Because scratche s~n ~he e~po~ed surface 14 interf~re wi~h 16 effective operation of this ice accumulation monitor~ it ifi 17 preferable that the exposed ~urfa~e 14 also be the e~posed 18 ~urface b~ a hard transparent layer 28~ as ~hown in f~gure~ 3t 8, 19 and 10, which will not be ~c:ratched or o~herwise damaged by 20 traff ic or other abusive el~ments, and which al~;o has an inde~ o~
21 refrac~ion grea~er than the index o~ reîraction o~ ice. 5uitable 22 mater ial~ ~or he hard transparen~ layer include sapphiEe a~d 23 ruby. :tn addition, the operation o~ the ice ac:cumu}ation monitor ~!4 15, i~ not changed i~ ~he entire prl m 17 is made from the hard mater i al; used preferably as the hard tran~parent layer 280 _ _, . _ _ _ . . . . , _ . . . . .
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~ ~7~3~3 ¦ ~lowever~ bec:au~e the hard materi~ 3 are typ~ ally more expen&iv~
2 ¦ than the prism mater~al and are u~ually more difficult to 3 ¦ machine~ llmiting the hard m2'cerial to a layer 15 pxeferable tO
4 ¦ making the enti e prism from the hard mal~e~lalb 5 ¦ To further pro~ect against eatpo~;ed~surfac~ damage in 6 ¦ appl~catlo~ uch as roadway~ and runway~3, a~ ~hown ln figure 8, ¦ ~he entire pri~m 17 may be mounted in a contaln~r 41 a~d 8 ¦ cushis)ned by ar~ elast~c m~terial 42 that maintain~ it~ ela~ticlty a~ low tempera~ure~ and ~ha~ deform~ ~o accommoda e agent~ that 10 mlght damage the exposed surfac~, then recover~ af'cer the 11 damagirlg agent pas e~O Suitable ela~tlc material~; for l;hi~
purpose include low tempera~ure silicon rubber~ eYpand d 13 polyethylene foams~ and clo~ed- cell~ high re~;illence polyur~3thane 14 f oam~ .
1~ Figure 8 also schema~ically show~ electrlcal connectlon6 16 from the laser diode/photodiode paclcage 18, a detector 19, and a 17 thermi~tor 22, ~o a cable connector 43, which cabl~ connecto~
18 connect3; ~h~e ice accumula~ ion moni~or components to an e~ter~al 19 cable 44 for c:o~ununication with the laser diode.:~photodlode drive ~0 control cirl::uit~ a ~eadout devic~ ~oz the detector, and a ~ceadout 21 dev~ce for the thermistor .

23 In ~he pr :Eerre~ embodiment ~h~ sloplng 6i~e ~6 o ~he pri~m is angled ~o th~t radiation emitted perpendicular ~o this side i8 24 incident at the expo~ed sur~ace 14 at an lllcident angle greater thar~ a~e but le~æ than 0c ~ ic:e -coYered ~ ~hi~ O

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: -1 the ~loplng s:ide facilitate~ mounting the emitter for effective 2 operation o~ thl6 ice accumulation monitor~ The other zloping 3 side 27 of ~he prl~m i~ angled ~o that radlatiorl re~lected frvm dy 'che bare e~:po~ed surace inter~ect~ thls ~ p~ng ~ide perpendiclllarly., Thi~ orlentation o~ the other ~loping 6ide 6 facilitates mountlng the detector 19 for ef~ective operation,, 8 A photodetector l9s c:omprised vf two separ~te radiat~on ~ detector~ 20 and 21~ i~ positioned within the prism 17, opposite f~om the emitter 18, and oriented ~o d~tect internally reflected 11 radiationO Alternatively~ the operation of thi6 ice accumulation 12 monitor i8 not chanl3ed ~y tbe use of two, separate, radiatioTI
13 detector~ whic:h are not housed in a ~ingle unlt. In addltion, 14 operation of thi~ lce accumulation monitor i8 not changed by positlonlng the photodetects)r on the ~loping prism surface 27t 03:
16 by transmitting the reflected rad~ation by optical fiber~ 39 to 17 e:Kternal photodetectors 40, as shown in f igure 6 .
18 A bandpa~s ~ilter 25 ~ with its bandpas~; waYelength centered 19 near the em~tter ~s dom~nant wavelens~th tran~mits r~flected radi~tion from the emi~ter, bu~` 8i9ni~Ei.oantly redures ~he amount 21 of ambient radiation reachir~g the rad1ation detec:tors 20 and 21~
22 so that possible nonlin~ar radiation detertor ' responses at very 23 high radiLa ion l~vel~ do not occur. The e~ect of ambient ~!4 radiatiorl ~B then ~liminated by pul~ing tbe emitter 18 and subtr~ctill~ detector respons~ obtained while lthe emitter i8 o~i~

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~ ' ~753~3 1 from res1pon~es obtained while the emltter i~ on.
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3 A ~emperature sensor 22, preferably located near the e:spo. ed 4 ~urface 14, i6 U ed I as di~cufi~ed hereafter under 5 ~_t_ D irl conjunctlon with response6 6 ~rom the two radiation det2ators to dl~tingui h betw~en 8 acs:umulation~ of wat~r and accumulation~ of ice. Tempera~ure sensor~ usable ~or this purpose inr:Lude t~ermocouples, R~Ds, solld ~ta~e temperature devices, and thermistor~. By way of 10 example, figure 9 shows a circuit diagram of a con~tant current 11 source driving a thermi~tor for use a~ a ~emperatllre sensor . The 12 6ame type of ~lrcuit 18 also applicable to RT3~o Alkernat~Lvelyt î3 a bridge oircuit mea6uring the resistance of the thermi&tor or 14 RTD, or other resistance-measurlng circuits fam:lllar ~:o ~hose 15 skilled in ~3lec ronic~ could be used to determine temperature 16 with a thermistor or an RTD . Standard voltage measuring 17 technigue~ could be used to determlne temperatures from volt~ge 18 measureme2lt~ s)n thermocouples or sol:ld 6tate devtces.
19 As dlscu~sed previously ir~ ~he section ~h~m~0 the 20 temp~rature ~en60r 22 also may be used a~ a con~rsl element ~or 21 temperature sensitive emit'Lers that do not have an integr~l mean~;
22 ~or maintaining ~emperature independent emis8ion in'cen6iti ~0 I~
;3 t.he temperature 81~n~ 1r i~; al80 u~ed a~; ~ control element, the 24 ~emperature sensor is located 80 that it i~ near both the emitt~
. and ~he exposed ~ur~ace,9 h~

_ __ _, __ ..... . . , . ~. __ .. ...
, ' . ' ,'. ' - ' , ' ': , ' '~ ' ' ' - ' ~ ~ ' . . . .
.

' ~ ' ' ' ~ ~7~ 3 2 ¦ AE; shown in f igure 10, when the ice acc:umulation monitor 15 3 ¦ i~ operated, a collima~ed beam of radiation 45 from th~ emitter 4 ¦ 18 ln~ers2cts the expo~ed surface 14 a~d ~L~ totally reflected 46 5 ¦ $f the e~po~ed ~urface is baIeq For clari. y i,n figure 10, beam~
6 ¦ o~ radiation are shown a~ respective rays 45~ 46, and 47. The 7 ¦ raaiation intensities d~tected by rad~ation detectors 20 and 21~
8 ¦ which are ~eparate section~ of photodetector 19r differ because ~ ¦ of the diferent positions, of 1;he~e radia~ion detectors 2û and ~1 îl) ¦ relative to the reflected rad~ation 46. A~ ic:e 48 accumulates on 11 ¦ the e~poaed ~urface 14y part of the emitted radlatiorl i~
12 ¦ tarn~mitlted ~nto the ice ~8~ and ~ubsequently reflected 47 at the ~3 ¦ ice-air lnterface 49, tbereby ~hiting tbe average effect of th~
14 ¦ re~lected radiation 46 and 47 towards the center of radlatio2l 15 ¦ de~es:tor 20, and ~lmultaneously ~ ting the ave~age e~fect of 16 ¦ the reflec ed radiation 46 and 47 from radiation de~ector 20 17 towards radlat;ion detector 210 Continued accumulation eventually 18 causes the aver~ge effec:t of the re~lected radia-ion to ~hift 19 pass radia~ion detector 2û ~o ~hat a maYimum oc:curs in the 20 re6po~se accumulation curve for radiatiorl de ec or 20.. The 21 response of rad~ation detector 21 i3 similar, but becau~e of the 22 d i~erent relative positions of radiation detectors 20 and 21, 23 the ma~imum for radiat~on de~ctor 21 occ:urs at 2 greater 24 accumulat~on tharl the maac :Imum ~or rad la~lon detes:~cor 20 . In f igu~ 1, the cu rve 51 5 hows a typ1oal reiponBe-eocumulition :

~ 3:~
-1 curve for radiation detecto.r 20" and the curve ~2 ~hows a typical 2 respon~e-accumulation curve for radiatlon det~r~tor 21.
3Calibration~ to obtain re~ponse -accumu~ ation ¢urve~ ~uch ~
a~51 and 52 are p~rformed by cal~brating radla'cion detector 5re~pon~e~ to kno~n accumulat i on~ of water ~. ~hifi iB poss~ble 6becau~e tbe inde:~ of refractiLon o:~ water i~ 1033 at the dominallt 7w~aveleng th emit~ed by the preferred eml'cter ~, and thi6 inde~s of 8refraction l~ practlcally the same a~ the index of refraction o~
lce,, 1.31~ at this wavelengtha 10Des$gn selections, ir~clu~ g t.he placemers'c of ~e 2mitter 1118, the placament of the radiation detec or~ 20 and 21, and lthe 12 l;rltensity of the emitted rad~atis:~n~ a~fect the 6hap~s6 and 13 locations of the calib~atlon c:l~rves with re~pect tv the re~pon~e-14 as::cumulation coordinate~, ~o with differe~t de~ign ~election~;, 15 different calibration cur~e~ will be obtained. ~owe~RrJ
16 regardless of the ~hap~ and location~ of the c:allbration curve~i~
17 once the c:allbration c:urve~ have been s)b'ca~ned~ interpretat~on, 18 a~ de6cribed h~raafter, of radiation decector r~spon~e~ in te~m~
19 of the calibrat~on curve~ serve~ to d~termine ~he amoun of ise 20 accumulated 3 21I~ the ln~erf ace between iC2 and a~r 49 ~s un~verl t ~uch als 22 might be cau~ed by ~u~Eace ice needles form~d du~lng fre~zing or 23 by surface damage of the ice caused by tra~f ic:, or i.~ ~e ice ha~
24 in~ernal defec~s such as ~racture c:raclc6 caused by traffic, the 25 e~fec~ o~ the re~les~ed radia~on 47 will ~e diffu~ed and .
' , . . . ; . ' .
' ' ' : ~ .

~7~3~3 1 orlented di~ferently from the effect of reflected radiatisn 2 tran~mi ted through perect ice with the ice-air interface 3 parallel to th~ e~posed ~urface 14 of the ice accumulat~on 4 monitor 150 Therefvre~ ~or any p~rticular accumulation of $ce, the respon~e of aach radiation detector~ 20 or 21, will depend on 6 the severity of ~urface distortion and the severity o~ i~ternal 7 defects~ Thereore, response-accumulatlon cur~es ~uch as 51 and 8 52 repre~ent re~ponse~ to accumulations of per~ect lce? orO
because tbe index of refraction of wa~er i8 practically the ~ame 10 a~ the lndex of re~raction of ice at the dominant wavelength emitted by the preferred emi~ter, accumulationc of wate~
12 ~owever~ becau~e o the po~sibility of ~urface di~tortion or 13 intgrnal defects, ~ny re~pon6e in a range between an upper l~mit 14 determined by curve~ such a~ Sl a~d 52t and a lower l$mit 15 determined ~y the response to a ~eYerely di~torted surface or a 16 severely damaged internal structure, w:l 11 be po~ible. Su¢h 17 limit~ are shown &Ghema~is:ally in f igure 11 a~ numeral~ 53 and 54 18 for upper and lower limi~ re~;pec~iYely for radiation detector 19 ¦ 20, and at numerals 55 and 56 ~or upper and 10WeE limits 20 ¦ respectively for radiation det~ctos 21, for a ~epre~entative 21 ¦ accumulation of ice, de~ianatad at numeral 57.
22 ¦ Becau~e of the po6~ibili~y of accumulatlo~ of flawed ice~
23 ¦ respon~e~ of th~ radlation detec~or~ do no~ determine unig~e ic~
2~ ¦ ~ccumulatlon~, Instead, each radiatlon detector re~pon~e 2S descr ibe6 a band of pO88 ible ice accumulation~, bou~ded by an .
~ .

~ 3~3 upper lce accumulaitorl limit and a lower ice accumulation limit,~
2 determln~d by the calibratlon c:urve~0 For e~ample, for radiation 3 detector 20 ~ he responE~e 6~ in f lgure 12 de~cribe~ a band of ice 4 accumulations bour1ded by an upper ice ~ccumulatlon limi. 63 and a 5 lowsr lc~ accllmulation limit 64. Likewi6e" for radiation 6 detector 21 l the response 65 de~cribe~ a band of ice 7 accumulat~ons bounded by an upper ic:e accumulation limit 66 and a 8 lc~wf~r lce accumulation l~mit 670 For any ice accumulation~
9 re~pon~e6 from rad iation detector~ 20 and 21 must be compatible 10 because both ~adiation detector~ are responding to the ~ame ice accumulatiot~p This compatibili y requ~rement res r~ctz 12 interpretation of ~hese re~pon6e~ to interpretation~ for whit:h 13 t~e ice accumulation bands overlap. For example~ the respor;se~
1462 for r~diation detector 20 ~nd 65 for radiation detector 21 l~i combine ~o lndicate an actual ice accumulatlon ln the range ~B in 16 f igure 12.
17In addition~ re6ponses from the radiation detector~ may 18 ~nclude a si~uation in which an i e ~ccumula'cion limit ~or one 19 ¦ radiatlon detector i8 the ~ame as an ice accumulation limit for 20 the other radiation detector,. 1:3camples o~ such a ~ltuation are 21~hown by the limlts 71 and 72 and the limits 73 and 74 in ~lgure 22 13. Th~ ~ituation can only occur for an acc:umlllation of watex 23 or of per~ect ice~. :E3ecau3e accumulations o~ per~ect ice are 24 ~ robable J thi~ ~ ituation . is normally interpreted a~ an 25 ac:cumulat~on ~f water, uslle~ the temperature s~ or indicates a , . - .

~ ~:7~i3~3 1 ¦ temperatllre less th~n the free:zing temperature of water. Then~
2 ¦ if the temperature ls leEi~ than the freezir:g temperature of 3 ¦ water, the c:or~b:lned response~ of radiation detectors 20 and 21 4 ¦ are lnterp~eted as lndlcatlng an accumulation in 'che range 5 ¦ determir~ed by the upper and lo~er ~ce ac:cumulation llmits.
6 ¦Salt on a pavement may lower the freezing temperature o~ the 7 ¦ water on the pavement t SO that water ~ ins~ead of ice ~ may be on 8 ¦ the pavement, even when ~he ~emperature ~ensor indicate~ a ¦ temperature below the fre~zing temperature of water. Elowever, ' 10 ¦ lnterpretation of the respon~e as ice in this ~nstance i~ a 11 ¦ s::on~ervative interpretation because lc:e will be indicated wher 12 ¦ the accumul~tion i~ actually unfrozen.
13 ¦Other mea~urements, such as impedance b~dge measurement~ of 14 ¦ the resi~tallc~ or tbe capacitance between elec~rcdes which would 15 ¦ be mounted flush with the eacpo~ed surface, c~n alAo be u ed in 16 ¦ con junction w~th re~ponBe~ from ~he r~diation detec:tors ~o 17 ¦ distingui~h accumulatiorl of lce from accumulations of water ~8 1 Therefore, although in this preferred f:mbod$merlt a temperature 19 ¦ ~ensor is used to ~ssist in d$~tinguishing arcumula~io~s of ice ~ ¦ from accumulations Df wate t operativn of thifi ice accumulation 21 monitor ~ not limited to an embodlment using a temper2ture 22 sensor ~OE this purpo ec ~3The ~ur~ace reflectivity o~ a ~oil- or mud-covered e~po~ed 24 ~r~e 14 i~ very low, ~o that when the expo~ed ~ur~ace beoomes ~5 coYered with ~oil or w~th mud~ nearly all of the emitted , ~ 3 ¦ radiation 1B transmltted lnto the ~oil or mud, instead of being 2 reflected a ~he expo6ed surface 14~ Ab~orptlon of radiation by 3 ~oil or mud ~ very high, ~o that after being transmi'c~ed into 4 the soil or mud on the e~posed sur~ace 1~ nearly all of the emitted 5 radlation is ab~orbed by the ~oil or mud,, ~herefore~ when the 6 e2~posed surfac~ i8 covered by ~o~l or by mud, tbe amount of 7 rad iation reflected to 'che radiation detector6 abruptly becomes 8 negllgible, be~ause ~uddenly nearly all o ti e emitted radiatlon 9 becomes ab~orbed by the ~oil or mud.
Responses from both radiation detec:t~rs will also be 11 negl~glble for very thick accumulations of lc:e. This . ~tuation 12 18 d~stlngui6hed from soil or mud depo~its by a g~adual decrea~e 13 in radiatiorl detectors~ xe~pon~es a~ ice accumulates, in c:ontra~t 14 with the abrupt decrease associated with ~oil or mud depo~ltsO
15 Theref ore the presence of ~o il 1 c~r mud on the e:~posed surf ace :14, 16 and the conseqllent need for cleaniRg the eYpo~ed surface, 1~
17 indica~ed by abrupt decrea~ef; in radiation detector re~pon~esO to 18 values whlch are also not greater than a charac:tPristic thre~hold 19 value ~or o~l or mude The thre~hold valu~ kha'c characte~i~e~ a 20 soil or mud-covered e~:po~;ed ~urface is determined by calibration 21 with soil- or mud covered e:Kpozed ~urace!; 0 22 The preceding discus~ n about in~erp~eting radaation 23 detector~ ' r~F:pon~es $~; incorpora~d into a series of logical 24 step6 to eliminate the ef~ect o~ amblent radiation on the 25 mea~ureDIent~ to indica~e and measure ~c:e accumula~iong~g ,' ~ ' . . - ' ~"' ..
- : .
.. ' ~ ' - , ' ' .

' 3:~
1 ~75 ¦ including accumulation6 of flawed ice~ to 8ignal when lce 2 ¦ accumulatlon has reached a critical th$ckne~8~ and to distlngui~h 3 ¦ accumulations of water from accumulation~ o~ i~e. By way of 4 ¦ example, such steps are indicated in figures 14a and 14b. Other 5 ¦ sequences of steps could also be ~Ised to interpret the radiation 6 I detectors' responses, but the sequence shown in figures 14a and 14b 7 ¦ contains the essential aspects of the interpretation. The interpre-B ¦ tation is perEormed humanly or electronically.
¦ The interpretat~on re~ulrez the respanse-ac:~umulation 10 ¦ calibrat~on curves; 51 and 52, temperature-sensor c:alib~ation ¦ data, and he ~oll/mud threshold value, herein iden~lfied by MIJD.
12 ¦ If it is desired to signal an ice accumulation warning for 13 ¦ a~cumulations greater than a c:ritlcal accu~nulation, a value ~or 14 ¦ this critical accumulation~ herei~ identi~ied by CRIT, mu~t also 15 ¦ b~ ~upplied"
16 ¦ If electronic interpretatlon i8 tD be performed ~ elther 17 ¦ tabular or an analytic representa~ion of the calib~ation curves 18 ¦ ls stored in memory prior to starting the interpretation Values 19 for MI~D and CRIT, an arbikrary value, ~, for C~?mparing presen~
20 ~and prev~ous values of correc~ed radia~ion detec'cors' respon~es,, 21 and an arbitrary value, ~, ~or comparing acll:umulation limlt~3" are 22 also ~tored ill memory . Fo~ manual interpretation ~ graphlcal or 23 analytic ~epre~entatiorls of the calibration~ will no~emally be 24 used 0 ~i Input data ~or the in'cerpreta ion a~e ~he ~cesponse o~

2-~

.
~ . .
, ': ' ' :
.
.~'' ' .

.

l ~2~53~3 - 1 ¦ radiation detes~or 20 while t:he emi~ter 1~3 of ~ ~ h~rein de~iynated 2 ¦ D9t and while the emitter i; on, herein de~;ignated Dlj t~e 3 ¦ respon~e o radlation detec~or 21 while t~ em~ter i~ off, 4 ¦ hereln deslgnated D10, and while the emitter i8 on~ be~el;rl 5 ¦ defilgnated D2; and the ~e pon6e of the temperature sensor, hereln 6 ¦ designated TEMP. In figures 14a and 14b these inpu~ data are 7 supplied from a readout device 77, such ~s a voltmeter, which is 8 switched between the output of radiation detector 20, 78, the output 9 o~ radiation detector 21, 79, and the output of the temperature 0 sensor, 80, to obtain the desired input data. In figur2 14a, responses from the ice accumulation monitor 15 are shown as being 12 transmitted by a data cable 44. In some situations it will be 13 preferable to transmit the ice accumulation monitor responses by 14 telemetry, and this can also be readily accomplished by those skilled in electronic data transmission.
16 Interpretation begins ~y as~3igning the value ~l-D~ 'co Vl and 17 the value D2-DlO to Y2, 81. Vl ~nd Y2 the~ repreE;ent detecto~
18 respon~e~ that haYe been correc~ed tv ellmir~ats the e~fect o~
19 ambient radiation . Subseque~t intea:pretation i~ based on Yl and 2() V2~, ~o ~e~e a~ignmentE; elimir;a~e the effect of amb~erlt 21 radiatiorl from the iLntarpretation0 22 The inte~pretation c:ontinue6 by dete~m~ning lf ~oil or mud 23 i8 pra~ent on tbe e:~po ed l3u~:Eace,D V~ and V2 are each compared 24 with the ~30~1~mud threshold value, 82 ~ 83, and i~ either Vl or Y2 ls greater than he threshold value, the interpretatio~ f~r ic:e .

, ~- ~ ' ., . ~ .
' . -~ , . ' ':
: ' :- ,' ' '~

~2~7~3~3 l c4n~cinue~0 If both Vl and V2 are les~ than the ol:L/mud 2 thre~hold ~ Vl and V2 are compared with heir values VlP and V2P
3 fram the previou~ cycle, 84, 85, to determine 1~ there ha~ been 4 an abrupt decrease in e~ ther Vl or V20 If there ha6 beerl an 5 abrupt decr~a~e in Vl or V2, a depo~it of ~oil or mud ~B
6 signalled 86. In figure 14 a depo~iit of soil or mud i8 ~iynall~d 7 a~ a diaplay on a monito~e 87. Alterna~ively a warning llght or 8 any Q her warnlng alarm could be actuated by the ~ollJmud 8i9n211~
After signalllng a deposit of ~o~l or mud, the interpretation 10 procedure ~top~ and awalts the cleaning ~d re~tartlng of the ice 11 accumulation morlitor.
12If there has noS been an abrupt decrea~e in either Vl ar V2, 13 or if eithgr Vl or V2 is greater than the threfiJhold value ~ the 14 interpretation continues by d~3term~ning the upper accumulation 15 bound, TMAX g and the lower accumulat lon boulld, TMIN. Vl ~8 16 compared with ~che calibration curve 51 for radiation detector 2 17 lto determ~Lne the ma~cimum accumulation a~i~oclated with Yl~ Tl~AX, 18 and the minimum accumulation a~soc ~ ated with Vl, Tl~IN~, 88.
19 Al~;o~ V2 is comparPd with the calibration s:~urve 52 ~or radiation 20detecto~ 21 to det~rmine the max1mum accumul2'cion a6~0ciated wlth 21 Y2, T2~iAX, and the minimum accumulation a~ociate~ with Y2~
22 T2~I~a, 89~ ~he upper accumula~lo~ bound i~ th~r~ tbe le~er .of 23 ~lPlP~X and T2NP.X ~ 90, and the lower accumulation .bound i~ the ~4 greater o~ Tlæ~IN and T2MIN, 91.
2~; . ~he interpretation then oontinue~ by dete~m~n~ng wheth~r the .. . ., _ , ' '"~ ' ' ~: . - ' .:
.

~ i3~

-1 accumulatis:)n i~ water or iC~13,. When water accumulates on the 2 e~posed Rurfac:e" tbe temperature i~ above freezlng, and one ~et 3 of accumulation bound~i ~or radiation detector~ 20 and 21 4 coincide~ such a~ 1DdiCa~ed by the ~oun~fi 71 and 72" or the bound~ 73 and 74 in figure 13" ~c:cumulation bound~ coincide i, 6 I, bo~h upper bound~ are the ~;ame, II, botb ~ owex bounds are it!be 8 same, or III ~ the upper bound ~rom one curve i5 the same as the lower bound flrom the o~her curv2. The~e po~ibili1;ies are checked 92~ 93, 94~ d lf, to withln a ~3mall differenc:e, ~, non~
of the accum~alation bounds are lthe ~ame d th~ accumulation s:an no .
11 be water~ Therefore an accumulatlon of ice is p~esent, and 12 e ither;
13 1. An ~ce accumulatiom and the upper ~nd lower 14 accumulat~orl bound~ are ~ignalled, 95~ and recorded and~or 15 di6played, a~ de6$red 87, and the procedure is read~ed for th~
16 next set of data 96; or 17 2~. The upp~r accumulation bound iL8 compared with tbe 18 c:ritis:al acGumulatlon,r CRIT, 97, a warnlng i8 ac~uate~ 98 i the 19 accumulation e~ceeds CRIT or the wiarning i~ not actuated i~ the 20 ¦ accumulation i~ le~ than CRIT~ and tha procedure ~s read~ed for 21 ¦ the next s~t o~ data 96~ or 22 3 " The~3~ alternatives alre combined ~o that upper and lower 23 accllmulation bounds are signall~d 95, and reco~ded and/or 24 d i~play~d, a~ de~ired 87, }le accumulation i~ evaluated ~o 25 determine lf it i; a critical ~ccumulation 97, a warnirg i~

ll 27 .. _, _ _ , . _ .. , , .. , . . . _ .. ....
.

, .

~53~3 1 ¦ actuate~ lf ~h~ ac:cumulation ea~ceedfi CR3:T 98 ~ and the procedure 2 ¦ i~ read ied for the ne~ set o~ d~ta 96 ~, 3 ¦ In figures 14a and 14b, the alterrlative of testing for a critical 4 ¦ accwnulation is indica-ted by dashed lines, and the occurrence of 5 ¦ a critical accumulation is shown as actuating an active highway 6 ¦ warniny sign 98. Instead of actuating a highway warning sign, 7 ¦ warning lights, horns, or othr alarms, could also be actuated, 8 ¦ to suite the needs of the particular application.
¦ If any o~ the accumulation bounds do coincide, t~e 10 ¦ temp~rature is checked 99 and if th~ temp~orature i~ great~r than 11 1 zero degr~e~ Cels:ius" wa~er i8 ~iignalled ~00" and an ppropriate 12 ¦ mes~age i~ di~played on a mon~tor 87. If the temperature i~ less 13 ¦ than zero de~ree~ Celsiui ~ an accumulation o~ ice 1~; present, arld 14 ¦ either.
15 ¦ l. An ic:e ac:cumulat~Lorl and the upper and lower 16 ¦ accumulal~ion bound~ are ~;ignalled 95, and xecorded and~or 17 ¦ di~played~ a~ d~3~ired 87, and the pro~edure i~ readied for the 18 ¦ next ~;et of data 96; or 19 ¦ 2. The upper accumulation bourad i~ co~p ~ed ~:Lth ~he ~ I c~itlcal accumulationO CP~IT~ 97" a wa~:n~ng ls actua~ed 98 if the 21 ¦ accumulatlon e~ceed~ CRIT or the wa~ng i~ not actua ed if the ¦ accumulatio~ less than CRIT, arld the procedure i~ ~eadied ~or 23 1 ~he next ~t o~ data 96; or 24 3,, ~hes~ alternatives a~e com~in~d 130 that upper and lower 25 at:e~.~ulaltivr~ bounds ara ~igr~alled 95~, and reco~ded arld/or 28 .

'. ~ . : ' ~ ' :

~ , . . .

,''- :. ~ .
.

~ ~t7~3~3 -1 displayed~ a des~red 87, the accumulation i~ eYaluated to 2 determine ~f it i6 a critical accumulatlon 97, a warning i~
3 actuated if the accumulation e~cgeds C~IT 98, and the procedure 4 i6 readied for ~h~ next ~et of data 96 a In addltion, inS~antaneou~ accumulation rate~, or average 6 accumulatlon rates ~or any de lred time int~rval~ can be readily 7 determined by storing m~asu~ed accumulation limits, taking 8 differences o accumulations, and divid$ng by the appropxiate time interval.
By using this ice accumulation monitor 15~ many pers4ns will 11 be rellably informed of when~ and how mucha ice is being formed~
12 generally in places and on 6urfacss wher~ it is not wanted9 and~
13 if de6ired, per~ons can be warned when critical accumulation 14 limlt~ are exceeded, informed of accumulation rate~ and warned when accumulation rat~s are dangerou~ Then appropriate mea~ures 16 can be taken to remove ~he lce or to mitigate against it~
17 consequencesO
18 ~
lg In addition~ o~al refl~c~ion at the bare eYposed ~urfac~9 with part~al transm$ssion at a covered e~posed surface and total 21 reflectio~ at the s~b~equent air interfaceO and calib~ation 22 curves similar to ~he responses 51 and 52 in figure 11~ will al~o 23 be ob~ained for accumulat~on~ of other transpar~nt ~ubs~3~ce~p 24 such a8 ethyl alcohol or ~.hyl ether~ whicb haYe inde~ sf refraction le~ than the index 3~ refraction of the ~ri~m.

-..

~ ~7Si33~3 3 ¦ Therefore, a~plic:al:lon of this accumula~ion monitor i6 not 2 ¦ re~tricted to measuring accumulation~ of ice or of water; but3 ¦ with calib~al:lons for th~se other 6ubstances, this accumulat1on 4 ¦ monitor will al~o mea6ure ~cs~umulatlons of the~e other sub~tanc:e~
5 ¦ and d istinguish accumula~is)n~ of the sol id form from 6 accumulations of the l~quidO

'10 lB
~9 ..

~3 2~

,, ~' . ~ '

Claims (30)

1. An ice accumulation monitor for detecting the formation of ice on a surface and measuring the amount of ice accumulated, comprising:

a) a prism that is transparent to radiation emitted by an emitter and with one surface of the prism exposed to ice accumulation and this surface positioned in the same plane as the surface on which ice accumulation is to be measured;
b) an emitter of pulsed electromagnetic radiation with means for maintaining the emission intensity independent of temperature, which emitter is oriented so that at the exposed prism surface the emitted radiation is totally reflected within the prism when the exposed prism surface is bare, but at the exposed prism surface the emitted radiation is only partially reflected within the prism when the exposed prism surface is covered with ice and the balance of the emitted radiation is transmitted into the ice layer and reflected at the subsequent ice-air interface;
c) two radiation detectors located to detect radiation reflected within the prism with one radiation detector located closer to the exposed surface than the other radiation detector; and d) a temperature sensor located in the transparent prism near the exposed surface, whereby upper and lower bounds of ice accumulation are measured by comparing outputs from each radiation detector with a calibration curve for that radiation detector.

2. An ice accumulation monitor, as claimed in claim 1, having a bandpass filter located with respect to the two radiation detectors and the exposed prism surface so that the amount of ambient radiation reaching the detectors is reduced, which bandpass filter has its bandpass wavelength centered near the dominant wavelength of the emitter.

3. An ice accumulation monitor, as claimed in claim 1, having the exposed surface made of a hard layer that is transparent to the radiation from the emitter.

4. An ice accumulation monitor, as claimed in claim 1, having the prism cushioned by an elastic material so that potential damage to the exposed prism surface is reduced.

5. An ice accumulation monitor, as claimed in claim 1, with the emitted radiation transmitted to the prism and directed at the exposed prism surface by an optical fiber so that at the exposed prism surface the emitted radiation is totally reflected within the prism when the exposed prism surfaces is bare, but at the exposed prism surface he emitted radiation is only partially reflected within the prism when the exposed prism surface is covered with ice and he balance of the emitted radiation is transmitted into the ice layer and reflected at the subsequent ice-air interface.

6. An ice accumulation monitor, as claimed in claim 1, with the end of an optical fiber at each radiation detector location and the reflected radiation transmitted by the optical fibers to the radiation detectors which are removed to locations exterior to the prism.

7. An ice accumulation monitor, as claimed in claim 2, having the exposed surface made of a hard layer that is transparent to the radiation from the emitter.

8. An ice accumulation monitor, as claimed in claim 2, having the prism cushioned by an elastic material so that potential damage to the exposed prism surface is reduced.

9. An ice accumulation monitor, as claimed in claim 2, with the emitted radiation transmitted to the prism and directed at the exposed prism surface by an optical fiber so that at the exposed prism surface the emitted radiation is totally reflected within the prism when the exposed prism surface is bare, but at the exposed prism surface the emitted radiation is only partially reflected within the prism when the exposed prism surface is covered with ice and balance of the the radiation is transmitted in the ice layer and reflected at the subsequent ice-air interface.

10. An ice accumulation monitor, as claimed in claim 2, with the end of an optical fiber at each radiation detector location and the reflected radiation transmitted by the optical fibers to the radiation detectors which are removed to locations exterior to the prism.

11. An ice accumulation monitor, as claimed in claim 3, having the prism cushioned by an elastic material so that potential damage to the exposed prism surface is reduced.

12. An ice accumulation monitor, or as claimed in claim 3, with the emitted radiation transmitted to the prism and directed at the exposed prism surface by an optical fiber so that at the exposed prism surface the emitted radiation is totally reflected within the prism when the exposed prim surface is bare, but at the exposed prism surface the emitted radiation is only partially reflected within the prism when the exposed prism surface is covered with ice and the balance of the emitted radiation is transmitted into the ice layer and reflected at the subsequent ice-air interface.

13. An ice accumulation monitor, as claimed in claim 3, with the end of an optical fiber at each radiation detector location and the reflected radiation transmitted by the optical fibers to the radiation detectors which are removed to locations exterior to the to prism.

14. An ice accumulation monitor; as claimed in claim 4, with the emitted radiation transmitted to the prism and directed at the exposed prism surface by an optical fiber so that at the exposed prism surface the emitted radiation is totally reflected within the prism when the exposed prism surface is bare, but at the exposed prism surface the emitted radiation is only partially reflected within the prism when the exposed prism surface is covered with ice and the balance of the emitted radiation is transmitted into the ice layer and reflected at the subsequent ice-air interface.

15. An ice accumulated ion monitor, as claimed in claim 4, with the end of an optical fiber at each radiation detector location and the reflected radiation transmitted by the optical fibers to the radiation detectors which are removed to locations exterior to the prism.

16. An ice accumulation monitor, as claimed in claim 5, with the end of an optical fiber at each radiation detector location and the reflected radiation transmitted by the optical fibers to the radiation detectors which are removed to locations exterior to the prism.

17. An ice accumulation monitor, as claimed in claim 7, having the prism cushioned by an elastic material so that potential damage to the exposed prism surface is reduced.

18. An ice accumulation monitor, as claimed in claim 7, with the emitted radiation transmitted to the prism and directed at he exposed prism surface by an optical fiber so that at the exposed prism surface the emitted radiation is totally reflected within the prism when the exposed prism surface is bare, but at the exposed prism surface the emitted radiation is only partially reflected within the prism when the exposed prism surface is covered with ice and the balance of the emitted radiation is transmitted into the ice layer and reflected at the subsequent ice-air interface.

19. An ice accumulation monitor; as claimed in claim 7, with the end of an optical fiber at each radiation detector location and the reflected radiation transmitted by the optical fibers to the radiation detectors which are removed to locations exterior to the prism.

20. An ice accumulation monitor, as claimed in claim 8, with the emitted radiation transmitted to the prism and directed at the exposed prism surface by an optical fiber so that at the exposed prism surface the emitted radiation is totally reflected within the prism when the exposed prism surface is bare, but a the exposed prism surface the emitted radiation is only partially reflected within the prism when the exposed prism surface is covered with ice and the balance of the emitted radiation is transmitted into the ice layer and reflected at the subsequent ice-air interface.

21. An ice accumulation monitor, as claimed in claim 8, with the end of an optical fiber at each radiation detector location and the reflected radiation transmitted by the optical fibers to the radiation detectors which are removed to location exterior to the prism.

22. An ice accumulation monitor, as claimed in claim 9, with the end of an optical fiber at each radiation detector location and the reflected radiation transmitted by the optical fibers to the radiation detectors which are removed to locations exterior to the prism.

23. An ice accumulation monitor, as claimed in claim 11, with the emitted radiation transmitted to the prism and directed at the exposed prism surface by an optical fiber so that at the exposed prism surface the emitted radiation is totally reflected within the prism when the exposed prism surface is bare, but at the exposed prism surface the emitted radiation is only partially reflected within the prism when the exposed prism surface is covered with ice and the balance of the emitted radiation is transmitted into the ice layer and reflected at the subsequent ice-air interface.

24. An ice accumulation monitor, as claimed in claim 11, with the end of an optical fiber at each radiation detector location and the reflected radiation transmitted by the optical fibers to the radiation detectors which are removed to locations exterior to the prism.

25. An ice accumulation monitor, as claimed in claim 12, with the end of an optical fiber at each radiation detector location and the reflected radiation transmitted by the optical fibers to the radiation detector which are removed to locations exterior to the prism.

26. An ice accumulation monitor, as claimed in. claim 14, with the and of an optical fiber at each radiation detector location and the reflected radiation transmitted by the optical fibers to the radiation detectors which are removed to locations exterior to the prism.

27. An ice a accumulation monitor, as claimed in claim 1, wherein water accumulation is distinguished from ice accumulation by nearly equal accumulation bounds combined with a temperature greater than zero degrees Celsius.

28. An ice accumulation monitor, as claimed in claim 1, wherein the response of each radiation detector is compared with a threshold radiation detector response that characterizes soil or mud accumulation and each radiation detector response is compared with previous radiation detector responses, to distinguish accumulations of soil or mud from accumulations of ice.

29. An ice accumulation monitor, as claimed in claim 1, wherein the effect of ambient radiation is eliminated from the measurements by subtracting the response of each radiation detector when the emitter is in the off portion of its cycle from the radiation detector response when the emitter is in the on portion of its cycle.

30. An accumulation monitor as claimed in claim 1 whereby upper and lower accumulation bounds of a substance other than ice are measured by comparing outputs from each radiation detector with a calibration curve for that substance and that radiation detector.