Wolf Wiesemann and Frank Lehmann, "Reliability of airborne CO2 DIAL measurements: schemes for testing technical performance and reducing interference from differential reflectance," Appl. Opt. 24, 3481-3486 (1985)
Remote measurements of trace species with a cw CO2 DIAL system suffer from errors caused by unknown variations of the target reflectivity with wavelength. Information on the mineral content of the ground gained by an airborne four-wavelength CO2 DIAL system can be used to correct remote trace species measurements performed by the same apparatus. Reflectance data in the CO2 laser spectral region for various rock and soil types are presented. The mineral content was determined by x-ray analysis. The technical performance of a two-wavelength airborne CO2 DIAL system was field tested by different methods, such as correlation techniques and comparison of target reflection data taken in the laboratory, and by remote measurements.
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The numbers are adjusted for the reflectance of a freshly deposited gold layer on a sandblasted plate. The standard deviation of the measurements (repeated on several days) is below 0.03.
The mineral contents are determined by x-ray analysis. Qz : quartz, Cb : carbonates, C1 : clay minerals, Mi : mica, Am : amphibols, Fp : feldspars
Table II
Influence of Target Grain Size on Reflection Coefficienta
Sample
I(A)/I(C)
9.2–9.7μm
10.2–10.7μm
Gneiss
0.97
0.92
Amphibolite
1.02
1.02
Granite
1.10
1.03 0.97
I(B)/I(C)
Sandstone
1.04
0.98
Maximum variation of normalized reflected intensity I(A, B, C) in the 9- and 10-μm bands for different grain size fractions. Fraction A: smaller than 1 mm, B: smaller than 200 μm, C: smaller than 20 μm.
Table III
Normalized Reflected Intensity of Farmland (Bare Soil) vs Quantity of Added Water
Total water content (ml)
Wavelength (μm)
Ratio 9.2/10.2
9.2
10.2
0
435
190
2.3
5
360
160
2.25
10
203
90
2.25
11
165
75
2.2
12
140
65
2.15
13
128
61
2.09
14
115
60
1.91
15
110
60
1.83
Tables (3)
Table I
Reflectance Measurements for Various Substances at 12C16O2 Wavelengthsa
The numbers are adjusted for the reflectance of a freshly deposited gold layer on a sandblasted plate. The standard deviation of the measurements (repeated on several days) is below 0.03.
The mineral contents are determined by x-ray analysis. Qz : quartz, Cb : carbonates, C1 : clay minerals, Mi : mica, Am : amphibols, Fp : feldspars
Table II
Influence of Target Grain Size on Reflection Coefficienta
Sample
I(A)/I(C)
9.2–9.7μm
10.2–10.7μm
Gneiss
0.97
0.92
Amphibolite
1.02
1.02
Granite
1.10
1.03 0.97
I(B)/I(C)
Sandstone
1.04
0.98
Maximum variation of normalized reflected intensity I(A, B, C) in the 9- and 10-μm bands for different grain size fractions. Fraction A: smaller than 1 mm, B: smaller than 200 μm, C: smaller than 20 μm.
Table III
Normalized Reflected Intensity of Farmland (Bare Soil) vs Quantity of Added Water