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Griggs, M.

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U	 SAI-75-666-LJ
November 1, 1975
L
DETERMINATION OF AEROSOL CONTENT
IN THE ATMOSPHERE FROM
LANDSAT DATA
Progress Report No. 3
Contract No. NAS5-20899
L D. Number 22260
Period Covered: August 1 to October 31, 1975
Principal Investigator: Dr. M. Griggs
Science Applications, Inc.
P. O. Box 2351
La Jolla, CA 92038
Prepared for:
Goddard Space Flight Center
In this third reporting period more theoretical calculations
were made, and Volz measurements were made at both test sites.
Theoretical Calculations
The Dave program was used to calculi : the radiance-aerosol
content relationship for MSS 4, 5 and 7. R was found in the calculations
for MSS 6 (see Progress Report No. 1) that the results for a size dis-
tribution with v = 4 agree closely with the measured radiance-aerosol
content relationship. Hence calculations for MSS 4, 5 and 7 were made
using v = 4, and refractive index of 1.5 + 01 .
The calculated relationships are shown in Figure 1 in com-
parison with the measured relationships. The measured and calculated
data were made to agree at N = 0 (1. e. a pure Rayleigh atmosphere) by
choosing the appropriate albedo in the theoretical calculations. The
values of A = 0, A = 0, and A = 0.005 for MSS 7, 6 and 5 respectively
look reasonable on the basis of published estimates of A (e. g. R. J.
Curran, Appl. Opt. 11, 1857, 1972). However, the value of A = 0.06
for MSS 4 appears high by a factor of 4 (compared to clear water), and
suggests that the measured radiance values in MSS 4 are influenced by
suspended matter in the water. Indeed, the MSS 4 wavelength (0.55 µm)
is one selected for chlorophyll observations (see R. J. Curran), and
is the channel which most clearly shows the presence of water turbidity
in the MSS data. Although the effective surface reflectivity appears
high, the slopes of the theoretical and measured relationships agree
very well, suggesting that for MSS 4 the reflectivity of naturally occur-
ring water is always significantly higher than that published for clear
water.
1
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6.26 5.5
Aerosol Content
Figure 1. Landsat 1 Data Compared to Theoretical Calculations
2
Water Vapor Effects in MSS 7 -- Figure 1 shows that most of the mea-
sured radiances for MSS 7 are lower than predicted by theory. This
is expected since there is significant absorption by water vapor in this
bandpass, which is not accounted for in the Dave program.
Pitts et al. (9th Remote Sensing Symposium, Ann Arbor, April
1974) calculated the atmospheric transmission for the MSS 7 channel as
a function of water vapor content. Their results, based on high spectral
resolution calculations, are shown in Figure 2, and agree well with band
model calculations by Marggraf and Griggs (J. Atmos. Sct. 26, 469, 1969).
The upwelling radiation traverses approximately (1 + sec 8) airmasses
where 8 is the sun zenith angle. Hence for the sun angle of 63.26'
(cos 8 = . 45), to which the radiance -aerosol content relationship is nor-
malized, the radiation traverses 3.2 airmasses. The Gutntck model
water vapor distribution has a vertical water vapor content of 1.7 cm, so
that the radiation traverses 5.5 cm with a transmission of 0. 81, according
to Ftgur a 2.
f	 .y
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nw	 N 1m
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Figure 2. Effect of Water Vapor on the ERTS MSS 7 Band.
3
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i
Of course, the actual water vapor content at the time of Landsat
data will deviate from the Gutnick model value. For typical water vapor
contents we might assume, from Figure 2, the transmission factor to be
applied to the MSS 7 data to be 0.85 ± 0. 1. However, since the present
investigation is basically empirical, and the range of transmission values
i 
p	
is small it is not considered necessary to adjust the MSS 7 radiance dataj
for water vapor effects.
O Uen Absorption in MSS 6 -- The MSS 6 bandpass includes the 0.76 µm
oxygen band so that the MSS 6 radiance will be reduced from that computed
by the Dave program which neglects oxygen absorption. Based on the
oxygen absorption data of Saiedy et al. (Appl. Opt. 4, 497, 1965) the ab-
sorption by oxygen in the MSS 6 channel is about 5% for 3.2 airmasses.
Since the oxygen concentration in the atmosphere is essentially constant,
its absorption has no significant effect on the present investigation.
Volz Measurem ents
In this period, it was possible to obtain Volz data for three of
the five Landsat 2 overpasses at the San Diego test site. One trip was
made to the Salton Sea test site and good data were obtained. Data were
also obtained for two Landsat 1 overpasses at San Diego. These Volz
data are given in Table 1.
Aircraft Measurements
No aircraft flights with the Exotech radiometer were made in
this period, since the Landsat digital data still have not been received
for comparison with the previous two sets of aircraft data. It is planned
to verify the usefulness of the aircraft measurements in conjunction
with the Landsat data before making further aircraft flights.
4
5
5
TABLE 1. Volz Data
'	 Date	 Aerosol Optical	 AerosolThickness	 Content
LANDSAT 2
San Diego	 8-21-75	 . 253	 1.19 N
	
9-26-75	 .284	 1.33 N
	
10-14-75
	 .136	 .64 N
Salton Sea	 10-31-75	 .116	 .54 N
LANDSAT 1
San Diego	 8-30-75	 .173	 .81 N
	
9-17-75
	 .193	 .91 N
The B&W prints were received and examined for the overpasses
coinciding with the aircraft measurements. The Salton Sea aircraft data
suggested that the water was polluted on 6-27-75 (see Progress Report
No. 2), but the B&W prints shows relatively minor pollution, in com-
parison with B&W prints of other overpasses. The B&W print for San
Diego on 7-16 -75 showed no evidence of pollution.
The aircraft measurements made at San Diego under hazy con-
ditions on 7-16-75 were analyzed, and found to show wide variability
In the radiance values. Correlating sharp peaks were observed in all
four channels with amplitudes as great as five times larger than the
mean value. These peaks had about 50 ft half widths, and are pre-
sumably due to sun glitter or patches of water with different reflecti-
vities. The amplitudes of the peaks did not appear to depend on the
F	 flight direction suggesting that sun glitter is not responsible. An
E ^
5
example of the data is presented in Figure 3, which shows the recordings
for MSS 4 and 5 obtained at 100 ft altitude over about a 1.6 mile flight
path (chart speed: 15 cm/min. ; airspeed: 90 mph). These data are in
sharp contrast to the smooth data of Figure 4, obtained at the Salton
Sea (6-27-75) under the same conditions. Visually, the water surface
appeared similar for both dates.
The spectral variation of the San Diego data based on mean
values for each run (about 1.5 miles) is shown in Figure 5. The data
show a slight tendency to peak at MSS 6, but not so clearly as at the
Salton Sea. MSS 4 and 7 show about the same radiance values, while the
MSS 5 and 6 values are generally lower at San Diego than at the Salton
Sea (compare with Figure 2 of Progress Report No. 2).
Further analyses of these data will be made when the Landsat
digital data are received.
Landsat Data
Digital data for three Landsat 2 overpasses at San Diego have
been received and analyzed; CCT's for three other overpasses at San
Diego and Sal" on Sea are on order. A CCT ordered for the Salton Sea
5-22-75 overpass (L D. 2120-17382) is not available since MSS 4 did
not produce acceptable data, and a CCT was not generated by NASA.
The radiance data analyzed to date are shown in Figure 6 as
a function of aerosol content. These data are based on calibration
data obtained from NASA-GSFC with the help of Mr. H. Qseroff, and
take into account the change in calibration made by NASA on July 16,
1975. The calibrations are quite different from Landsat 1, in that
there is an offset at zero count, t. e. , at zero count the radiance has
6
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Figure  3. San Diego Aircraft Data 7-16-75.
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	 Mz t
Figure 5. San Diego Ocean Radiances
Measured from Aircraft 7-16-75
a small but significant value. The equations relating radiance R
(mw/cm2/µn• 'sr) and counts C are given in Table 2.
It should be noted that, since the CCT's do not print negative
count values, that the current system does not allow for radiances
below . 06 mw/cm 2/µm/sr. It is seen from Figure 1 that for Landsat 1
MSS 6 and 7 there were 12 values less than this. This apparent limi-
tation in the Landsat 2 data will be further evaluated.
TABLE 2. Radiance-Count Relationships
MSS 4 R	 = .8 +.2008C 
MSS 5 R	 = .6 + .1339C
MSS 6 R	 = .6 +. 1150C 
MSS 7 R	 = .61 + . 3360C
9
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Figure 6. Landsat 2 Radiance vs. Aerosol Content
10
1In Figure 6 the Landsat 2 data do not show the same re-
lationships as Landsat 1 (Figure 'I). However, only three overpasses
have been analyzed to date, and further evaluation of the data will be
made when more overpasses are analyzed.
Plans
Volz data will be taken at both test sites, weather permitting.
Analysis of the digital data will continue, and the calibration procedures
will be further evaluated.
SIGNIFICANT RESULTS
Where are no significant results to report in this period.
PUBLICATIONS
No publications were made in this period.
RECOMMENDATIONS
No changes in the program appear necessary at the present
time.
DATA USE
Value of Data	 Value of Data	 Value of Data
Allowed
	 Ordered
	
Received
$ 6500.	 $ 1806.	 $ 1206.
PROBLEMS
No problems exist at the present time.
11


Determination of aerosol content in the atmosphere from Landsat data

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