Polarimetric Remote Sensing of Aerosols over Land

Journal Article · Mon Jan 26 04:00:00 EST 2009 · Journal of Geophysical Research. D. (Atmospheres), 114(D01206)

DOI:https://doi.org/10.1029/2008JD010619· OSTI ID:949083

Waquet, F; Cairns, Brian; Knobelspiesse, Kirk D; Chowdhary, J; Travis, Larry D; Schmid, Beat; Mishchenko, M

The sensitivity of accurate polarized reflectance measurements over a broad spectral (410 -2250 nm) and angular (±60° from nadir) range to the presence of aerosols over land is analyzed and the consequent ability to retrieve the aerosol burden and microphysical model is assessed. Here we present a new approach to the correction of polarization observations for the effects of the surface that uses longer wavelength observations to provide a direct estimate of the surface polarized reflectance. This approach to surface modeling is incorporated into an optimal estimation framework for retrieving the particle number density and a detailed aerosol microphysical model: effective radius, effective variance and complex refractive index of aerosols. A sensitivity analysis shows that the uncertainties in aerosol optical thickness (AOT) increase with AOT while the uncertainties in the microphysical model decrease. Of particular note is that the uncertainty in the single scattering albedo is less than 0.05 by the time the AOT is greater than 0.2. We also find that calibration is the major source of uncertainty and that perfect angular and spectral correlation of calibration errors reduces the uncertainties in retrieved quantities compared with the case of uncorrelated errors. Finally, in terms of required spectral range, we observe that shorter wavelength (< 500 nm) observations are crucial for determining the vertical extent and imaginary refractive index of aerosols from polarized reflectance observations. The optimal estimation scheme is then tested on observations made by the Research Scanning Polarimeter during the Aerosol Lidar Validation experiment and over Southern California wild fires. These two sets of observations test the retrieval scheme under pristine and polluted conditions respectively. In both cases we find that the retrievals are within the combined uncertainties of the retrieval and the Aerosol Robotic Network Cimel products and Total Ozone Mapping Spectrometer Aerosol Index that we are comparing to. This confirms the validity of the sensitivity analysis of the polarized reflectance observations to the aerosol number density and microphysical model and demonstrates the unique capability to accurately retrieve aerosol optical depths under pristine conditions and also the single scattering albedo of aerosols at higher optical depths.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (US)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 949083
• Report Number(s): PNNL-SA-61581; KP1701000
• Journal Information: Journal of Geophysical Research. D. (Atmospheres), 114(D01206), Journal Name: Journal of Geophysical Research. D. (Atmospheres), 114(D01206) Vol. 114; ISSN 0747-7309
• Country of Publication: United States
• Language: English

Related Subjects

47 OTHER INSTRUMENTATION
54 ENVIRONMENTAL SCIENCES
AEROSOLS
CALIBRATION
POLARIMETERS
POLARIZATION
REFRACTIVE INDEX
REMOTE SENSING
SENSITIVITY ANALYSIS
WAVELENGTHS