Airborne measurements of areal spectral surface albedo over different sea and land surfaces

Abstract

[1] Airborne measurements of the ratio of spectral upward and downward irradiances (so-called spectral albedo) are used to derive the areal spectral surface albedo in the wavelength range from 330 to 1670 nm. The data were collected over different sea and land surfaces in cloudless atmospheric conditions during three field campaigns. Measurements from the Albedometer (developed at IfT) and the NASA Solar Spectral Flux Radiometer (SSFR) are employed. Spectral radiative transfer calculations show that atmospheric scattering and absorption within the layer beneath the flight level considerably contribute to the airborne albedo measurements reported here, even for low flight altitudes (0.2-0.5 km). To remove this atmospheric masking, a nonlinear extrapolation of the airborne albedo measurements to the ground is performed. The nonlinearity is due to the vertically inhomogeneous distribution of the particle microphysical properties. This fact underlines the importance of aerosol profile measurements for the proper correction of atmospheric masking. Examples of the extrapolated areal spectral surface albedos are discussed in terms of their solar zenith angle dependence, their small-scale, and general variability. Finally, typical areal spectral surface albedos for different sea and land surfaces, as derived from the three measurement campaigns, are supplied in parameterized form for use in radiative transfer applications.

Spectral absorption of biomass burning aerosol determined from retrieved single scattering albedo during ARCTAS

“…where F calc is modeled actinic flux, F meas is the measured actinic flux, z 0 is the surface, z flight is the aircraft altitude and ↓ and ↑ denote downwelling and upwelling, respectively (Wendisch et al, 2004). Modeled actinic flux values were determined using TUV 5.0 and SSA and AOD values calculated using the scattering and absorption in-situ data described above.…”

Influence of spatial heterogeneity of local surface albedo on the area-averaged surface albedo retrieved from airborne irradiance measurements

“…Bowker et al, 1985;Feister and Grewe, 1995;Aoki et al, 2002;Wuttke and Seckmeyer, 2006) deliver the local surface albedo data for point locations only, whereas satellite measurements cover larger areas (Schaaf et al, 2002). On an intermediate scale, airborne radiation measurements deliver the retrieved area-averaged surface albedo ρ ret (Webb et al, 2004;Wendisch et al, 2004;Coddington et al, 2008;Bierwirth et al, 2009).…”

“…Combined with effects due to multiple scattering, this leads to a "smearing" (averaging) of the surface albedo as seen by the downward looking airborne irradiance instrument. Thus, the agreement between the area-averaged surface albedo ρ ret retrieved by the method of Wendisch et al (2004), based on airborne measurements and the heterogenous local surface albedo ρ loc , depends on the flight altitude and aerosol properties. Since many remote sensing applications need knowledge about ρ loc instead of ρ ret , this paper investigates how well the surface albedo can be spatially-resolved by airborne measurements depending on the heterogeneity of the local surface albedo and flight altitude.…”

“…1). In a first step, the sea albedo is fixed to 0.026 following Bowker et al (1985) at λ = 450 nm, whereas the land albedo is varied with respect to different reflectivity properties to test various sea-land surface albedo ratios δ. used to retrieve ρ ret (z flight ) following the method described by Wendisch et al (2004). Exemplarily, Fig.…”

Comparing Airborne and Satellite Retrievals of Optical and Microphysical Properties of Cirrus and Deep Convective Clouds using a Radiance Ratio Technique

“…SMART measured spectral upward radiance . The irradiance data can be used to determine the spectral surface albedo (Wendisch et al, 2001;Wendisch and Mayer, 2003;Wendisch et al, 2004). An active stabilization system keeps the optical 15 inlets in a horizontal position during aircraft movements of up to ± 6°from the horizontal plane (Wendisch et al, 2001).…”