Data collection platforms (DCP's) are being used at a Black Hills, South Dakota, test site (MMC 226A) to record radiometric measurements needed to determine solar and atmospheric parameters that affect ERTS-1 multispectral scanner radiance measurements. A total of 72 channels of analog data transmitted from an unattended ground truth site via three DCP's at least six times a day. The system has operated with only minor problems since September, sending forth daily measurements of biophysical responses and atmospheric conditions. Comparisons of scene radiance data calculated from ERTS images with that measured on the ground show the image-measured values to be 35 percent higher for the green channel and 20 percent higher for the red channel for the same scene targets. Radiance values for channels 6 and 7 are nearly the same from the ground data and from the imagery

Weber, F. P.

English

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DCP-COLLECTED ABSOLUTE TARGET REFLECTANCE SIGNATURES 
ASSIST ACCURATE IMTERPRETATION OF ERTS-1 IMAGERY 
Frederick P. Weber, Pacific Southwest Forest and Range Experiment Station, 
Forest Service, U. S. Department of Agriculture, Berkeley, California 94701 
ABSTRACT 
Data collection platforms (DB's) are being wed at  a 
8l.ack H i l l s ,  South Dakota, test s i te  (bMC 226A) t o  record 
radiometric measurements needed to  determine solar and at- 
mospheric parameters that affect  Ems-1 multispectral scan- 
ner radiance measurements. 
A to ta l  of 72  channels of analog data are transmitted 
from an unattended ground t ruth si te via three DB's a t  
least s i x  times a day. ?he system has operated with only 
minor problems since September, sending forth daily mea- 
surements of biophysical responses and atmospheric condi- 
tions. Comparisons of scene radiance data calculated from 
ERTS images with that  measured on the ground show the image- 
measured values to  be 35 percent higher for  the green chan- 
nel and 20 percent higher for  the red channel for  the same 
scene targets. 
nearly the same f r o m  the ground data and f r o m  the imagery. 
Radiance values f o r  channels 6 and 7 are 
1. INTKIWCTION 
The Forest Service investigation in  the Black H i l l s  of South 
Dakota focuses on monitoring forest  stress i n  the ponderosa pine 
(Pinus ponderosa Laws .) ecosys t e m  using coordinated data collected 
from ERTS 1, aircraf t ,  and f r o m  ground instrumentation. ?he cause 
of the stress being monitored i n  the Black Hills is a widespread 
epidemic of the mountain pine beetle (Dendroctonw nderosae Hopk.) 
the northern Black H i l l s  this past year as identified-on high-flight 
aerial photography obtained in  September 1972 after the dead trees 
' were ful ly  discolored. lhe infestation spots identified ranged i n  
size from single trees t o  many hundreds of trees w i t h  the greatest 
number of trees occurring in  infestations having 11 t o  25 trees. 
May 1972 for  the purpose of measuring radiometric responses of the 
principal components of the ecosystem i n  relation to  changing atno- 
spheric and environmental conditions. Our primary concern w a s  t o  
?he bark beetle was responsible for  over 10,000 i n  f=- estation spots i n  
Establishment of an ERTS 1 intensive study si te w a s  begun during 
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Qriglnal photography may be 
- n.-,*e&,I 
https://ntrs.nasa.gov/search.jsp?R=19730019633 2020-03-17T08:50:39+00:00Z
provide closeup spectral radiometric ground truth of the relation be- 
tween healthy ponderosa pine and the trees which were under stress f r o m  
attack by the mountain pine Beetle. Figure 1 shows the location of the 
intensive study si te in  the Black Hills. I t  was deemed important to 
monitor spectral radiometric information on two additional ecosys tem 
components--(I) open pastures and grasslands which occupy the majority 
of nonforest land in  the Black Itills and (2) so i l  and rock outcrops 
which provide the targets of greatest reflectance contrast with the 
forest. The rock outcrops provide important control points because 
they are eas i ly  identifiable within the forest on small-scale imagery. 
Many biophysical and atmospheric parameters were measured through- 
out the t e s t  site, but the most important was absolute target reflec- 
tance. 
radiance as measured with our RS-2 ERTS-1-matched spectral radiometers 
shown in  Figure 2 .  
over each of four locations within the study s i t e  (over healthy pine, 
beetle-killed pine, grassland pasture, and rock outcroppings) . Each 
instrument w a s  positioned a t  the top of an instrument tower i n  a way 
that would provide a clear vertical  [downward-looking) view of the 
target from a height of 7 meters (m). 
In practice, the RS-2 spectral radiometers provide continuing 
information of importance in  each o.f the ERTS mdtispectral scanner 
(MSS) bands for  each of the ecosystem targets. Figure 3 shows the 
calibrated radiance output a t  5 levels for  each radiometer detector. 
Due to the s l ight ly  different spectral responsivities of each detector- 
f i l ter  combination, there is a different calibrated radiance for  a 
given neutral density level. 
detector response was measured for each channel as a function of 
changing target exitance, with target exitance being the energy in  
watts per unit area of each target. 
i n  Figure 5 are for unamplified signals from Pin 10 DP detectors with 
a 10' field-of-view. In operation the output signals from each of 
the spectral radiometer channels is amplified with a m-101 (M) a t  a 
gain of 10 before entering the recording system. 
w i t h  the RS-2 radiometers, additional data collected include net a l l -  
wave radiation and upwelling shortwave radiation. A t  one central lo- 
cation, instruments measure the spectral components of damwelling 
radiation, atmospheric water vapor content, temperatures, and wind- 
speeds. 
data recording fac i l i ty  where sensor signals are amplified and &ti- 
plexed for broadcast over the ERTS data collection system (D(1s) via 
These data were obtained in  terms of scene radiance and ir- 
One of the 4-channel radiometers was positioned 
For the calibration data (Figure 4) ,  the 
Detector response levels shown 
In addition t o  recording target reflectances a t  each test s i te  
Instrumentation data from all four sites are wired into a central 
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three data collection platform (DB's) (Figure 6) .  
nels of data are multiplexed over 24 DCP channels. A t  the same time 
that instrumentation data enter the DCP buffers they are recorded in 
parallel on a digital data acquisition system,. As the instrumentation 
laboratory is located within the forest, it was necessary to mount the 
DCP antennas a t  the top of a 32 m instrumentation tower, as shown i n  
Figure 7. 
Two sa te l l i t e  images of the Black Hills were selected for the pur- 
pose of scene correlations between ground truth data and ERTS MSS scene 
radiance data. Scene 1047-17175 provides clear coverage of the western 
Black H i l l s  for September 8, 1972, on MSS channels 4, 5, and 7. Scene 
1065-17175 provides partially open coverage of the north-central Black 
H i l l s  on Septenber 26, 1972, when a l l  channels of the MSS were working 
well. Figure 8 shows a black-and-White rendition of a 4-channel color 
composite created on our 1% color reco6iner for the Septenber 26 data. 
For the purpose of scene radiance analysis of the E R E  image, m i -  
crodensitometer scans were made of several transects on each image and 
al l  available spectral bands. 
radiance for each 70 mm bulk data scene using calibration data taken 
from the 1 5  step wedge on each scene. 
September 26 scene are shown by the white lines on Figure 1. Radiance 
data were correlated to  scene points using proportional distances from 
control points which could positively be identified on both the satel- 
l i t e  images and the FB-57 small-scale photography. 
In all ,  72 chan- 
Scan densities were converted to scene 
Several of the scans made on the 
3. RESULTS 
In the past we have received incomplete seasonal radiometric data 
It is clear that a significant 
for the Black Hills because of the large expense i n  manning tes t  site 
instruments over long periods of time. 
benefit of EIiTS is having the DCS capability for continuously monitoring 
f ie ld  instruments and being able to send current and accurate data to 
our office hundreds of miles away from the remote field s i te .  
minimum of three day-time transmissions of f ie ld  data seems adequate for 
monitoring cr i t ical  biophysical responses and environmental conditions. 
I t  seems a simple matter to  add a few totalizing circuits p existing 
instrumentation so as to better ut i l ize  the three nighttime data t 
missions. 
Tne 
As a result of daily monitoring of Black Hills rqdiometric instru- 
ments we are now beginning to get a clearer picture of spectral enera. 
relationships in the ponderosa pine ecosystem over time. For example, 
Table 1 shows haw albedo of the rock outcroppings was unchanged from 
September 8 t o  26, whereas the albedo of the pasture increased 3 per- 
cent. 
decrease while bark beetle-killed pine increased by 1 percent. 
During the same period healthy ponderosa pine showed a 1 percent 
In 
1515 
addition to Wowing trends, the implication is that we now know for  
any satellite scene the re la t ion  of absolute qeflectances between dif- 
ferent ecosystem components. ' 
Table 1. The relationship between albedos is shown fo r  four Black 
.Hills ,  South Dakota, ecosystem components at the time of 
two EKI'S 1 passes i n  Septenber. 
Target Sep tede r  8 S e p  tenS>er 26 
Percent Albedo' 
Healthy pine 11 10 
Pasture  grass 19 22 
Rock outcrop 24 24 
Stressed pine 15 16 
L 
Albedo is the r a t i o  of upwelling to  downwelling shortwave 
radiation 
Scene radiance data obtained f r o m  the September 8 imagery of the 
Black Hills is.sholKn in Table 2. 
Table 2. Black Hills scene radiance data fo r  September 8, 1972, are 
derived f r o m  microdensitometer analysis of black-and-white 
70 mm bulk data positives 'for scene 1047-17175. 
Scene Radiance ( m i l  1 iwa t ts / cmL -SR) 
MSS Channel1 
Target 4 5 7 
Healthy pine 
Stressed pine 
Lake 
Rock outcrop 
Mecadum road 
Concrete highway 
Mine tailings 
N m  logging road 
Tornado area 
0.333 
0.344 
0.339 
0.418 
0.394 
0.339 
0.354 
0.333 
0.414 
0.188 
0.229 
0,200 
0.270 
0.194 
0 i 239 
0.249 
0.243 
0.300 
0.847 
0.983 
0.657 
1.218 
0.953 
1.062 
1.170 
1.014 
1.206 
1 
Imagery received fo r  damel 6 was  unusable because 
of the large number of data dropouts 
1516 
The 70 mm bulk imagery was ful ly  adequate for  extracting the scene 
radiance signatures of some ecosystem targets such as healthy ponderosa 
pine and rock outcroppings , using precision microdensitometry. 
even be t te r  nunbers can be calculated for  some of the hard-to-pinpoint 
targets l ike bark beetle infestation areas when the 9 1/2-inch black- 
a n d - h i  te bulk imagery becomes available. 
When it became apparent that we were not going to  get ERTS-1 
imagery of the Black Hills that was free of clouds over the ent i re  
study area during 1972, w e  se t t led  on the September 26 scene for  in- 
tensive analysis. 
enhancements of the enlarged color recombination were photographed on 
color transparency f i l m  (Figure 8) and placed i n  a VARISCAN viewer for  
scene point correlation. 
quality ecosystem scene point recognition when the image was  enlarged 
to  a viewing scale of 1:32,000 on the VARISCA?? screen. ?his was a 
useful step i n  becoming familiar with scene points before measuring 
the scene radiance w i t h  the microdensitometer scans. Table 3 shows 
the calculated scene radiance f o r  the September 26 imagery of the Black 
Hills. 
However, 
We have examined color reco inations of this  scene 
created t o  optimum illumination levels i n  our 9 I S viewer. The best  
Significantly, we  were able to retain good 
Table 3. Black Hills scene radiance data for  September 8, 1972, 
are derived f r o m  microdensitometer analysis of black- 
and-white 70 nun bulk data positives f o r  scene 1065-17175. 
Scene' Radiance (milliwatts/un2TiQ- 
Target 
MSS Channel 
4 5 6 7 
Healthy pine 0.154 0.087 0.158 0.392 
Stressed pine 0.140 0.093 0.144 0.399 
Pasture grass 0.214 0.148 0,239 0.601 
Mecadum road 0.213 0.105 0.173 0.440 
Rock outcrop 0.316 0.204 0.353 0.920 
Open p i t  gold mine 0.250 0.170 0.311 0.805 
Golf course 0.217 Q.156 0.244 0.628 
The significance of scene radiance calculations on the MSS imagery 
is i l lus t ra ted  i n  Table 4 where they are compared to  scene radiance 
measurements made of similar ecosystem targets on the ground which were 
transmitted to  us by the DCS. It is noteworthy that here we are get- 
t ing the first data which show .the effect of amsphere  on radiance 
values as measured on imagery when compared to that which exists near 
the ground. Prior t o  this time we have only had predictions of what 
1517 
should happen with gemkalized conditions. We see the greatest effect 
of atmosphere on MSS channel 4 where there is an bverall 30 plus per- 
cent increase i n  scene radiance on the sa te l l i t e  imagery. For the 
ifrfrared channel 7 them is lbss than 10 percent overall difference 
in measured values, with the ground-measured radiance being the hi&r. 
Table 4. The relationship is shown between scene radiance data 
measured on ERTS-1 imagery (scene 1065-17175) and 
that measured on the ground i n  the Black H i l l s  by the 
RS-2 spectral radiometers. 
Scene Radi ance (milliwatts/cm'-SR) 
MSS Channel 
4 5 6 7 
Target E K E  Ground ERITS Ground EHTS Ground EHTS Ground 
Healthy pine .154 . lo2 .087 ,065 ,158 .179 .392 ,468 
Stressed pine .140 ,093 .093 :lo1 ,144 ,135 .399 ,506 
Pasture grass ,214 .141 ,148 .159 .239 .280 .601 .646 
b c k  outcrop ,316 .219 ,204 .199 .353 ,358 ,920 .999 
4. DISCUSSION 
From p.l'eliminary work kith ERTS-1 imagery we look forward with 
great expectation3 to receiving one good summertime image of the entire 
Black H i l l s  test site under fu l l  sun conditions. Having already learned 
to analyze imagery gathered under less than optimun conditions, there 
is colisiderable reason-for wanting additional good quality coverage 
so that we can accomplish the goals of the study. Data presented in  
this report were analyzed from two Septeder ERTS-1 images. One image 
covered only a small portion of the study area and one MSS channel 
malfunctioned. The other image was obtained on a cloudy day when the 
atmospheric water content was high (relative humidity measured a t  the 
test s i te  a t  the time of the sa te l l i t e  overflight was 82 percent). We 
anticipate few problems in  the continued operation of the DB's and 
the data collection system. 
1518 
FIGURE 1. A PORTION OF THE, BLACK HfLLS FOFOSTRY TEST S I T E  SHOWS 
SOME OF THE MICRODENSITOMETER SCAN LINES 
FIGURE 2. RS-2 SPECTRAL RADIOMETERS 
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1.0 I I I I - - - CALIBRATED SPECTRAL RADIANCE FOR RS.2 DETECTORS WITH CONSTANT 
1W.W STANOARD LAMP AN0 4 NEUTRAL DENSITY LEVELS 
- 
- - - 
50% MAX. 
28% MAX. 
16% MAX. 
0.1 
4 'I. MAX. 
QO1 
- +- - - - - 
W 0
f 
2 
(L 
t 1 
0.001 I I I .  I I 
1 2 3 4 
CHANNEL NUMBERS 
FIGURE 3. CALIBRATED SPECTRAL RADIANCE FC)R RS-2 DETECTORS 
FIGURE 4. TARGET EXITANCE VERsZrs DETECTOR RESPONSE FOR RS-2 RADIOMETERS 
1520 
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1521 
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DCP-collected absolute target reflectance signatures assist accurate interpretation of ERTS-1 imagery

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