Multispectral imaging and analysis system

3 4

FIG. 2 is a schematic block diagram illustrating ex- Each detector in an array has characteristics that may

emplary electronics that may be used in connection be different from every other detector. The differences

with the detector elements in each array for the purpose in characteristics reside primarily in the dark current

of normalizing output signals provided by the detectors. appearing as a DC offset and the inherent gain of the

FIGS. 3 and 3B illustrate a pair of graphs presenting 5 detector. Accordingly, the DC offset and the gain of

spectral reflectance data for certain unaltered and al- each individual detector in an array must be normalized,

tered rock samples, respectively. Referring to FIG. 2, an exemplary circuit that is

FIG. 4 is a schematic diagram illustrating a circuit suitable for normalizing the DC offset and gain of CCD

that may be used to implement an exemplary algorithm detectors or a conventional line array is illustrated. As

for analyzing spectral reflectance data such as is pres- 10 shown, the output of each detector 40 is applied to a

ented by FIGS. 3A and 3B. preamplifier 42 the output of which is applied as one of

two inputs to a differential amplifier 44 via a first input

DESCRIPTION OF THE PREFERRED lead 46. Assuming that the input signal applied to the

EMBODIMENT second input lead 48 of the differential amplifier 44 is

Referring to FIG. 1 of the drawings, solar energy at 15 initially zero, then the initial output of the detector 40 various wavelengths is reflected from terrain under from an image made while the lenses are capped can be observation and is received by an imaging system thus applied to an A to D converter circuit 50 and therethrough a plurality of lens systems 4, 6, 8 and 10. Data after aPPued to a memory 52 for storage. Normalization in the form of electrical signals which are provided at can thus be accomplished by having the dark current the output of the imaging system 2 may be applied via 20 f°r ■? detectors stored and thereafter subtracted from an appropriate electrical cable 12 to a computer or det<for signal coming from Uluminated terrain, micro-processor 14. The data output of the micro- Hence' *e 0UtPut <*the mem0ry 52 m?y therfffter ^ processor 14 may thereafter be applied in the form of aPPhed th?>uSh a ? *A cSvertf J"""*54 TM the suitable video signals to an infonnation recorder and ^ second of two mputs to the differential amplifier 44 via display unit 16 via an appropriate cable 18 for recorda- ^gj ^ a ... the dafk current on an /or l p ay. memory data is subtracted from each detector signal

As shown, the lenses 4 6 8 and 10 may each be pro- ^ . ^ovided when the detector is Uluminated and

vided with a changeable filter 20 22, 24 and 26 respec- ^ fa tfa normalized.

lively. Such filters 20, 22^24 and 26 serve to limit mc- M ^ UbaaA ^ ^ ... n fce ...

dent radiation transmitted through the corresponding normalized b a feed forward arrangement m which the

lens to preselected bandwidths chosen for use m the gaincmTentofthe ... ^igap*liedfromtfaeAto

analysis of data. ,,„...„ . D converter circuit 50 to a gain current memory 56 and

It is clear that the various lenses 4,6,8 and 10 may be t0 a divider circuit 58 which sefves tQ effectively nor.

of a conventional type and may be even replaced by an 35 the inherent gain of the detector 40 by dividing

optical system havmg a single lens which is followed 0utputted signals by the inherent gain,

optically by dichroic plates and lenses ma configuration ^ output of the divider circuit 58 would hence

similar to a color television camera wherein incident represent a normalized data output of the detector 40

light is split up into several primary colors for applica- which may ^ thereafter applied as an input to the com

tion to a plurality of color vidicons, in this case detector ^ pUter or micro-processor 14.

arrays. It is understood that all of the circuits discussed and

In the imaging system 2 shown in FIG. 1, each of the described heretofore with respect to FIG. 2 may be

lens systems 4, 6, 8 and 10 have associated therewith a conventional circuits, that are commercially available

separate CCD array 28, 30, 32 and 34. The outputs of ^ Gf a type that are well known in the prior art as to

the respective CCD arrays 28, 30, 32 and 34 may be 45 structure, operation and use.

appropriately connected electrically to a preamplifier it js noted that the dark current memory 52 and the

and signal conditioning system 36 which shall be de- gain current memory 56 may each be a small portion of

scribed in greater detail in connection with FIG. 2. a much larger memory circuit of conventional type that

Timing logic circuitry 38 of conventional design may may be used for the purpose of storing all of the data

be used in a manner well known in the prior art to have 50 from each of the detector arrays 28,30,32 and 34. In the

the data read out from the individual detector arrays in event that a single memory is used for such purpose it

parallel. must of course be assumed that the capacity of the mem

Conventionally, CCD arrays that are presently avail- 0ry is sufficiently large to accommodate storage of all of able may include 160,000 detector elements in a 400 X the data and other signals to be used for detector signal 400 array. Such CCD arrays may be thermo-electrically 55 normalization as has been heretofore discussed. It is cooled in a conventional manner. The present intended noted that the present state of the art permits any numapplication utilized four arrays 28, 30, 32 and 34 which ber of different procedures to be used for the purpose of are registered such that the same element located on accomplishing storage and/or retrieval of data in data each array receives radiation reflected from the same memory circuits, and any of the conventional techpoint on the targeted terrain. Information or data would 60 niques may be used as may be appropriate, be concurrently read out of each of the four CCD ar- With the exception of the memory circuits 52 and 56, rays 28, 30, 32 and 34 in parallel, that is, from corre- it may be regarded that the circuitry of FIG. 2 be a part sponding detector elements at the same time. The mean of the imaging system 2 that has been described in confer triggering each array to have data from successive junction with FIG. 1.

detectors outputted is well known in the art and there- 65 Referring now to FIGS. 3A and 3B, graphic presen

fore is not considered required to be explained in detail tations of spectral reflectance data for unaltered samples

herein. Data that is retrieved or outputted by the CCD A and B, and altered samples A and B are illustrated. It

arrays is analyzed by being applied to the computer 14. may be observed that the graphs pertinent to the unal5 6

tered and altered samples A may be readily distin- material being sought as well as its location on the ter

guished. The same holds true for the Samples B. Of the rain being covered by the airborne imaging system

several methods by which such graphs can be distin- would thus be indicated.

guished, taking certain ratios of the data values at prese- Operationally, the optical units 4, 6, 8 and 10 are

lected wavelengths is effective, accurate and possible to 5 mounted and aligned to have each of the arrays 28, 30,

be accommplished expeditiously. Selected wavelengths 32 and 34 optically stacked and registered at infinity,

are noted by the vertical lines indicated by the numerals When so registered, paralax is not considered to present

20, 22, 24 and 26 which correspond to the filters earlier a significant problem when the system is operated at a

referred to in conjunction with FIG. 1. It is anticipated reasonable altitude; i.e. 10,000 feet or higher,

that such filters 20,22,24 and 26 may each have a band- 10 . .^ the system m accordance with the subject

width of 0.02 microns and be centered at wavelengths invention is by m traveling at 140 miles

of 0.55 microns, 0.70 microns, 0.85 microns and 1.0 ^ houf ^ at m ... of l0 OQQ feet> the mstanta_

microns, respectively, neous field of view of each detector is approximately

Keternng to wu 4, a quasi-logic circuit representmg 2QQ which

corresponds to a resolution of

anexemplary algorithm which serves to implement die 15 Q fi ffle ... ^

above-mentioned calculation and comparison of ratios . ,. . . . . ..

to known data sets is shown. The algorithm may be J^T? f. aP?f ^te * ?50 "fTM Per houf j*

„„.-,„ „,„„,„m„„j • t„ „ „,;„,„ „ ° „„„ „ ' _ 40,000 feet will provide a resolution of approximately

readily programmed into a micro-processor or com- <»«♦/•♦ 1

puter 14. It is anticipated that, each algorithm be con- "meters/picture element.

structed in the form of an interchangeable microcircuit 20 A l\1810 * understood that the use of charge coupled

memory element devices of conventional type now available commer

The output of a detector from the array 28 associated cMv ^limit the operational bandwidth of the subject

with the filter 20 would be ratioed with the correspond- svstem to wavelengths accommodated by the detectors,

ing detector output of the array 30 associated with the i e > °-4 to 10 microns.

filter 22. Similar ratios are formed between detector 25 It is to be understood that although a square detector

outputs for the arrays 30 and 32 and detector outputs for array nas been described and discussed in the foregoing

the arrays 32 and 34. The calculation of such ratios may description, line arrays may be used equally well. When

be readily accomplished by the use of conventional a line array is used, rather than having a target picture

divider circuits 59, 61 and 63. taken at predetermined intervals, data would be contin

It is of course understood that such ratios simply 30 ually read out of the line array associated with each

provide an indication of the slope of the graphic data optical unit as it is swept across the target area beneath

between data points corresponding to the filters 20,22, the aircraft or satellite.

24 and 26. Increasing the number of different filters and From the foregoing discussion it is now clear that the

hence data points would, increase the accuracy of the subject invention provides an imaging and analysis sys

analysis. However, the use of four filters is anticipated 35 tem whereby spectral reflectance data may be collected

to be sufficient for most cases. by an airborne system and immediately processed in

The ratios produced are compared to known values real time such that the data can be also displayed in real

by having the ratio data signals applied to comparator time and recorded for future use. Clearly, the subject

circuits 60, 62 and 64. In this manner, the slope of data invention provides a compact system which is economi

graphs being analyzed can be accurately compared to 40 caUy useable to provide data on an immediate basis as

known data graphs for materials likely to be observed. compared to prior art systems which require a user to

As is well known in the prior art, the comparator cir- wajt a period of several months before having the col

cuits 60, 62 and 64 may include the use of threshold data made available for yet subsequent expensive

circuits which serve to provide output signals only analysis by having the data applied to general purpose

where a ratio value falls between pre-determined 45 ...

b°unds- . „ , While a preferred embodiment of the present inven

The outputs of the comparator circuits 60,62 and 64 ^ has been described hereinabove, it is intended that

may thereafter \k| applied as inputs to an AND gate 66 ^ matter ... m ^ above description and shown

A «°U^ ?? * C M 8 ?^ H <n m the accompanying drawings be interpreted as illustra

collected data favorably compares to a known standard. 50 .. , 0 ..f . „

Analyzed data would; be thereafter applied via the fe *** not mt a lumtf * m f^^'

cable 18 from the computer 14 to the monitor and film ^ons' instructionsi and^arrangements which fall within

recorder 16 for displacing and recordation for future th^°ff **. of the mventlon mav be made

use as shown in FIG. 1 What is claimed ,s:

Referring again to FIG. 1, the monitor 16 may be 55 !: A svstem forf receiving and analyzing incident

equipped to have applied thereto visible terrain data radiation reflected from the earth s surface m real time,

which may be provided from any of the optical units 4, wmch svstem *mable for geographic surveying from

6, 8 and/or 10. Such visible terrain data may simply be airborne vehicles, said system comprising:

unprocessed data from any of the optical units. As may imaging means for receivmg said incident radiation,

be desired, an additional camera may be used to provide 60 said imaging means including:

visible terrain data. a plurality of detector arrays maintained in opti

The monitor and recorder unit 16 may thus be used to cally stacked registration, said detector arrays

display both the visible terrain data, as well as the spec- each including an array of charge coupled de

tral reflectance data, for the sample being sought. When vices wherein said charge coupled devices of

spectral reflectance data is superimposed on the visible 65 each said array are maintained in registration

terrain data and displayed, materials or conditions being with corresponding devices in every other array,

sought and located may appear as dark spots or areas on said arrays providing detector signals indicative

the display of visible terrain data. The presence of such of radiation incident thereon,