The mass of particulates in a vertical column of dust outflow from northwestern Africa is derived with the aid of satellite measurements of nadir radiance. The measurements were made from the Landsat-1 satellite. Measurement accuracies are discussed. A radiative transfer model with a known mass of dust is developed to account for the measured radiance values. The model is constructed with knowledge of a few values of optical parameters measured from a surface ship. The accuracy of the model is discussed. The resulting mass of particulates smaller than 10-μm radius in a vertical column is 1.6 g m−2.
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Signal-to-Noise Ratios for the MSS Observations over the Oceana
SNR
0.5–0.6 μm
0.6–0.7 μm
0.7–0.8 μm
0.8–1.1 μm
Lower confidence limit
44
26
14
7.7
Average
49
28
16
8.4
Upper confidence limit
52
30
17
9.1
Preflight
38
30
23
7
The values apply to single observations where the instantaneous field of view is approximately 80 m in diameter at the ground. The 90% confidence limits are given. The preflight values are the indicated test values for one channel, which are given in Ref. 1, p. A-12, for the compression mode in the first three bands and for the linear mode in the 0.8–1.1-μm band.
Table II
Nadir Radiance of the Ocean–Atmosphere as Measured by MSS at 21.2° N and 17.6° W on 9 August 1972, 11 h 05.1 min GMTa
0.5–0.6 μm
0.6–0.7 μm
0.7–0.8 μm
0.8–1.1 μm
Radiance N in mW cm−2 sr−1
0.553
0.334
0.203
0.326
Solar constant S in mW/cm2
17.23
14.75
12.04
24.22
Reflectivity R
0.118
0.083
0.062
0.049
The solar zenith angle θ0 = 31°.
Table III
Nadir Reflectivity Measured over Various Bodies of Water by the MSS from Landsat-1a
Place
Date
Solar zenith angle
Reflectivity at nadir
0.5–0.6 μm
0.6–0.7 μm
0.7–0.8 μm
0.8–1.1 μm
Atlantic Ocean 21.2° N 17.6° W
9 Aug. 72
31°
0.114
0.081
0.060
0.048
Pacific Ocean San Diego
14 Sept. 72
40°
0.108
0.060
0.039
0.023
Lake Tahoe Elevation 1899 m
25 July 72
32°
0.052
0.021
0.013
0.003
Pacific Ocean data were supplied by H. Al-Abbas and the Lake Tahoe data by L. T. Darby.
Table IV
Surface Data Measured at Ship Discoverer at 21.0° N and 17.2° W on 9 August 1972a
Surface wind
Time
Direction
Speed (msec−1)
06 GMT
30°
13
1200
20°
9.3
1800
360°
9.3
Vertical optical thickness (base e) of the atmospheric particles
Normal Optical Thicknesses of the Model Atmosphere and Its Constituents
Constituent
0.5–0.6 μm
0.6–0.7 μm
0.7–0.8 μm
0.8–1.1 μm
Scattering gases
0.098
0.050
0.028
0.013
Scattering particles
0.497
0.483
0.479
0.444
Absorbing gases(ozone, oxygen, water vapor)
0.027
0.021
0.050
0.205
Total
0.622
0.554
0.557
0.662
Table VI
Effective Reflectivity for the Lambert Model to Give the Correct Contribution of the Surface Illumination to the Nadir Radiance Above the Atmospherea
Band
0.5–0.6 μm
0.6–0.7 μm
0.7–0.8 μm
0.8–1.1 μm
R
0.046
0.041
0.036
0.036
θ0 = 31°. Surface wind speed = 9.3 msec−1.
Table VII
Sources of Error in the Radiance of the Ocean–Atmosphere Systema
Relative error in %
Measurement
15
Computations
difference between methods
4
layers too thick optically
5
neglect polarization
2
computational error sum
11
Model parameters
sea surface reflectance, ΔR = 0.01
8
Rayleigh optical thickness
0
ozone
1
particulate optical thickness, ΔτA = 0.025
1
slope, Δν = 0.25
2
real index of refraction, m = 1.3333
−4
imaginary index of refraction, −0.01i
−8
particle shape
−4
log-normal size distribution
2
model root-sum-square error
13
Total root-sum-square error of computations and model
17
The solar zenith angle θ0 = 31° and Δλ = 0.5–0.6 μm.
Tables (7)
Table I
Signal-to-Noise Ratios for the MSS Observations over the Oceana
SNR
0.5–0.6 μm
0.6–0.7 μm
0.7–0.8 μm
0.8–1.1 μm
Lower confidence limit
44
26
14
7.7
Average
49
28
16
8.4
Upper confidence limit
52
30
17
9.1
Preflight
38
30
23
7
The values apply to single observations where the instantaneous field of view is approximately 80 m in diameter at the ground. The 90% confidence limits are given. The preflight values are the indicated test values for one channel, which are given in Ref. 1, p. A-12, for the compression mode in the first three bands and for the linear mode in the 0.8–1.1-μm band.
Table II
Nadir Radiance of the Ocean–Atmosphere as Measured by MSS at 21.2° N and 17.6° W on 9 August 1972, 11 h 05.1 min GMTa
0.5–0.6 μm
0.6–0.7 μm
0.7–0.8 μm
0.8–1.1 μm
Radiance N in mW cm−2 sr−1
0.553
0.334
0.203
0.326
Solar constant S in mW/cm2
17.23
14.75
12.04
24.22
Reflectivity R
0.118
0.083
0.062
0.049
The solar zenith angle θ0 = 31°.
Table III
Nadir Reflectivity Measured over Various Bodies of Water by the MSS from Landsat-1a
Place
Date
Solar zenith angle
Reflectivity at nadir
0.5–0.6 μm
0.6–0.7 μm
0.7–0.8 μm
0.8–1.1 μm
Atlantic Ocean 21.2° N 17.6° W
9 Aug. 72
31°
0.114
0.081
0.060
0.048
Pacific Ocean San Diego
14 Sept. 72
40°
0.108
0.060
0.039
0.023
Lake Tahoe Elevation 1899 m
25 July 72
32°
0.052
0.021
0.013
0.003
Pacific Ocean data were supplied by H. Al-Abbas and the Lake Tahoe data by L. T. Darby.
Table IV
Surface Data Measured at Ship Discoverer at 21.0° N and 17.2° W on 9 August 1972a
Surface wind
Time
Direction
Speed (msec−1)
06 GMT
30°
13
1200
20°
9.3
1800
360°
9.3
Vertical optical thickness (base e) of the atmospheric particles