Use of satellite data to study the surface and cloud properties and the solar radiation
budget (SRB) is very important for improving our understanding of cloud and sea-ice
albedo feedback in the Arctic. Based on an accurate and comprehensive Radiative
Transfer Model (RTM), algorithms were developed for using the National Oceanic and
Atmospheric Administration (NOAA) Advanced Very High Resolution Radiometer
(AVHRR) data for the discrimination of clouds from snow/ice surfaces, retrieval of snow
albedo, and retrieval of cloud optical depth and effective droplet size.

Through the improved estimation of solar reflectance in AVHRR channel 3 (3.75 micron)
and anisotropic correction, albedo in channel 3 is derived. The albedo and a threshold
function for the albedo were used for automatic cloud discrimination from snow/ice surfaces.
Thin cirrus was discriminated using the brightness temperature difference between
AVHRR channels 4 and 5 and brightness temperature in channel 4. The AVHRR-derived
cloud cover fraction is in good agreement with SHEBA surface visual observation.

Retrieval of snow grain size and mass-fraction of soot from AVHRR is difficult
because of the effects of aerosol in channel 1 and the strong water vapor absorption
in channel 2. Retrieval of surface albedo is more promising. With the melt of snow/ice,
different narrow-to-broadband conversion relations are found and its use can improve
the estimation of broadband albedo. The derived albedo is in good agreement
with SHEBA surface observation of albedo.

AVHRR channels 2, 3 and 4 are used to retrieve cloud optical depth, effective cloud
droplet size and cloud top temperature simultaneously. Validation wih in-situ aircraft
measurements by the NCAR C-130 and the NASA ER-2 and with surface measurements
obtained during the SHEBA experiment indicates that the error in the retrieved effective
droplet size is less than 10%, but the retrieved optical depth ptical depth can be as large
as 50 to 80% due to uncertainty in (1) the satellite-measured radiances, (2) partial cloud
cover, and/or (3) vertical inhomogeneity. Under partially cloudy conditions, the satellite-retrieved
cloud optical depth is larger than that derived from surface-measured downward solar
irradiance by 40 to 130%, and the Downward Surface Shortwave Radiation (DSSR)
derived from satellite-derived optical depth is found to be underestimated by as
much as 30%, depending on cloud cover fraction. Overestimate of satellite-derived
opticel depth is mainly due to the high reflectivity in AVHRR channel 2 over snow/ice
surfaces, the presence of partial cloud cover and inaccurate representation of the
scattering phase function for mixed-phase clouds.