J. Mao (mao@qhearts.gsfc.nasa.gov) is with Science Systems and Applications, Incorporated, 10210 Greenbelt Road, Suite 400, Lanham, Maryland 20706. USA
S. R. Kawa is with the Atmospheric Chemistry and Dynamics Branch, NASA Goddard Space Flight Center, Greenbelt, Maryland 20771. USA
Jianping Mao and S. Randolph Kawa, "Sensitivity studies for space-based measurement of atmospheric total column carbon dioxide by reflected sunlight," Appl. Opt. 43, 914-927 (2004)
The feasibility of making space-based carbon dioxide (CO2) measurements for global and regional carbon-cycle studies is explored. With the proposed detection method, we use absorption of reflected sunlight near 1.58 μm. The results indicate that the small (∼1%) changes in CO2 near the Earth’s surface are detectable provided that an adequate sensor signal-to-noise ratio and spectral resolution are achievable. Modification of the sunlight path by scattering of aerosols and cirrus clouds could, however, lead to systematic errors in the CO2 column retrieval; therefore ancillary aerosol and cloud data are important to reduce errors. Precise measurement of surface pressure and good knowledge of the atmospheric temperature profile are also required.
You do not have subscription access to this journal. Cited by links are available to subscribers only. You may subscribe either as an Optica member, or as an authorized user of your institution.
You do not have subscription access to this journal. Figure files are available to subscribers only. You may subscribe either as an Optica member, or as an authorized user of your institution.
You do not have subscription access to this journal. Article tables are available to subscribers only. You may subscribe either as an Optica member, or as an authorized user of your institution.
You do not have subscription access to this journal. Equations are available to subscribers only. You may subscribe either as an Optica member, or as an authorized user of your institution.
Optical Characteristics of Aerosols and Cirrus Cloud Used in the Radiance Calculationsa
Aerosol Type
τ
ω
g
Maritime
0.13
0.98
0.72
Rural
0.05
0.81
0.64
Urban
0.33
0.52
0.63
Cirrus
0.14
0.73
0.8
τ is the optical thickness, ω is the single-scattering albedo, and g is the asymmetry factor.
Table 2
List of Baseline Input and Output Parameters of Radiance Simulations
Input
Output
1976 U.S. Standard Atmosphere, 0–120 km
Band coverage, 6315–6385 cm-1
CO2 level, 360 ppmv
Scanning function, triangular
Lambertian surface with reflectance, Rs = 0.3
Spectral resolution (FWHM), 0.07 cm-1
lowtran background aerosols
Spectral sampling step, 0.035 cm-1
Solar zenith angle, 30°
Satellite viewing angle, nadir
Table 3
Direct Beam Idir, the Sum of Scattered Radiances Isct = Ibsct + Isrfl + Irsct + Imsct, and the Total Back-to-Space Radiances Itot at a Pair of Adjacent Off-Line and On-Line Channels Near the R-Branch Center and the Off-Line/On-Line Radiance Ratios for Baseline Clear-Sky and Cirrus Cases, Respectively, and the Sensitivity of the Ratio to the Cirrusa
Channel
Baseline
Cirrus
Idir
Isct
Itot
Idir
Isct
Itot
Off line (νoff)
5.0292
0.2308
5.2600
3.7085
1.1248
4.8333
On line (νon)
0.9159
0.0406
0.9565
0.6754
0.1985
0.8739
Ratio (R)
5.4910
5.6847
5.4992
5.4908
5.6665
5.5307
Sensitivity (%) (ΔR/Rbaseline)
0.573
The reference atmospheric CO2 concentration is 360 ppmv. The off-line frequency νoff is 6359.45 cm-1 and the on-line frequency νon is 6359.98 cm-1. The radiance unit is in mW m-2 cm sr-1.
Table 4
Same as Table 3 but for Cirrus Asymmetry Parameter Perturbation Runs
Optical Characteristics of Aerosols and Cirrus Cloud Used in the Radiance Calculationsa
Aerosol Type
τ
ω
g
Maritime
0.13
0.98
0.72
Rural
0.05
0.81
0.64
Urban
0.33
0.52
0.63
Cirrus
0.14
0.73
0.8
τ is the optical thickness, ω is the single-scattering albedo, and g is the asymmetry factor.
Table 2
List of Baseline Input and Output Parameters of Radiance Simulations
Input
Output
1976 U.S. Standard Atmosphere, 0–120 km
Band coverage, 6315–6385 cm-1
CO2 level, 360 ppmv
Scanning function, triangular
Lambertian surface with reflectance, Rs = 0.3
Spectral resolution (FWHM), 0.07 cm-1
lowtran background aerosols
Spectral sampling step, 0.035 cm-1
Solar zenith angle, 30°
Satellite viewing angle, nadir
Table 3
Direct Beam Idir, the Sum of Scattered Radiances Isct = Ibsct + Isrfl + Irsct + Imsct, and the Total Back-to-Space Radiances Itot at a Pair of Adjacent Off-Line and On-Line Channels Near the R-Branch Center and the Off-Line/On-Line Radiance Ratios for Baseline Clear-Sky and Cirrus Cases, Respectively, and the Sensitivity of the Ratio to the Cirrusa
Channel
Baseline
Cirrus
Idir
Isct
Itot
Idir
Isct
Itot
Off line (νoff)
5.0292
0.2308
5.2600
3.7085
1.1248
4.8333
On line (νon)
0.9159
0.0406
0.9565
0.6754
0.1985
0.8739
Ratio (R)
5.4910
5.6847
5.4992
5.4908
5.6665
5.5307
Sensitivity (%) (ΔR/Rbaseline)
0.573
The reference atmospheric CO2 concentration is 360 ppmv. The off-line frequency νoff is 6359.45 cm-1 and the on-line frequency νon is 6359.98 cm-1. The radiance unit is in mW m-2 cm sr-1.
Table 4
Same as Table 3 but for Cirrus Asymmetry Parameter Perturbation Runs