Chapter 16
Satellite Remote Sensing of
Evaporation over Sea
Peter Schliissel
University of Colorado at Boulder
Colorado Center for Astrodynamics Research
Boulder, CO 80309-0431
USA
Abstract
The remote sensing of evaporation over sea mainly requires to derive three quantities from
satellite data: Sea surface temperature, surface wind speed and specific air humidity. The sea
surface temperature is derived from infrared imagery of the Advanced Very High Resolution
Radiometer (AVHRR), flown on the NOAA polar orbiters and from the Along Track Scanning
'~adiometer (ATSR) operated on the ERS-1 satellite. Split- and dual-window techniques are
employed in order to COFCct the satellite-measured brightness temperatures for atmospheric
effects, mainly due to Vlia.",er vapour. Recent techniques include non-linear terms and information from other radiometers improving the retrieval accuracy. Attention must be paid to the
difference between bulk and skin surface temperatures which can be as great as ±lK due to
the skin cooling and the diurnal thermocline. This difference is of the order of the retrieval
accuracy achieved nowadays and must be known when interpreting satellite-derived sea surface
temperatures. Surface wind speed and near-surface humidity are obtained from passive microwave measurements of the Special Sensor Microwave/Imager (SSM/I) that is part of the DMSP
satellite series. While the surface wind speed is derived from brightness-temperature variations
induced by emissivity changes in resposne to surface roughness and foam coverage the determination of the surface air humidity is related to the water-vapour columns that can be retrieved
from multi-channel retrieval schemes applied to the satellite-measured microwave data. Recent
investigations show that the SSM/I not only allows to retrieve the total precipitable water
but also the water-vapour column of the lower 500 m which is closer related to the surface air
humidity than the total water-vapour column. The retrieval methods are developed by means
of radiative transfer simulations and subsequent multivariate analysis. An application of the
theoretically developed techniques to real satellite data and comparisons with in-situ measurements are performed to test the single parameter retrievals. A subsequent intercomparison of
t,le latent heat fluxes der,'
Radiation and Water in the Climate System:
Remote Measurements
Edited by Ehrhard Raschke
© Springer-Verlag Berlin Heidelberg 1996
Satellite Remote Sensing of
Evaporation over Sea
Peter Schliissel
University of Colorado at Boulder
Colorado Center for Astrodynamics Research
Boulder, CO 80309-0431
USA
Abstract
The remote sensing of evaporation over sea mainly requires to derive three quantities from
satellite data: Sea surface temperature, surface wind speed and specific air humidity. The sea
surface temperature is derived from infrared imagery of the Advanced Very High Resolution
Radiometer (AVHRR), flown on the NOAA polar orbiters and from the Along Track Scanning
'~adiometer (ATSR) operated on the ERS-1 satellite. Split- and dual-window techniques are
employed in order to COFCct the satellite-measured brightness temperatures for atmospheric
effects, mainly due to Vlia.",er vapour. Recent techniques include non-linear terms and information from other radiometers improving the retrieval accuracy. Attention must be paid to the
difference between bulk and skin surface temperatures which can be as great as ±lK due to
the skin cooling and the diurnal thermocline. This difference is of the order of the retrieval
accuracy achieved nowadays and must be known when interpreting satellite-derived sea surface
temperatures. Surface wind speed and near-surface humidity are obtained from passive microwave measurements of the Special Sensor Microwave/Imager (SSM/I) that is part of the DMSP
satellite series. While the surface wind speed is derived from brightness-temperature variations
induced by emissivity changes in resposne to surface roughness and foam coverage the determination of the surface air humidity is related to the water-vapour columns that can be retrieved
from multi-channel retrieval schemes applied to the satellite-measured microwave data. Recent
investigations show that the SSM/I not only allows to retrieve the total precipitable water
but also the water-vapour column of the lower 500 m which is closer related to the surface air
humidity than the total water-vapour column. The retrieval methods are developed by means
of radiative transfer simulations and subsequent multivariate analysis. An application of the
theoretically developed techniques to real satellite data and comparisons with in-situ measurements are performed to test the single parameter retrievals. A subsequent intercomparison of
t,le latent heat fluxes der,'
Radiation and Water in the Climate System:
Remote Measurements
Edited by Ehrhard Raschke
© Springer-Verlag Berlin Heidelberg 1996