Abstract
Abstract. A new method to detect cloud-free snow-covered areas has been developed using the measurements by the Advanced Along Track Scanning Radiometer (AATSR) on board the ENVISAT satellite in order to discriminate clear snow fields for the retrieval of aerosol optical thickness or snow properties. The algorithm uses seven AATSR channels from visible (VIS) to thermal infrared (TIR) and analyses the spectral behaviour of each pixel in order to recognize the spectral signature of snow. The algorithm includes a set of relative thresholds and combines all seven channels into one flexible criterion, which allows us to filter out all the pixels with spectral behaviour similar to that of snow. The algorithm does not use any kind of morphological criteria and does not require the studied surface to have any special structure. The snow spectral shape criterion was determined by a comprehensive theoretical study, which included radiative transfer simulations for various atmospheric conditions as well as studying existing models and measurements of optical and physical properties of snow in different spectral bands. The method has been optimized to detect cloud-free snow-covered areas, and does not produce cloud/land/ocean/snow mask. However, the algorithm can be extended and able to discriminate various kinds of surfaces. The presented method has been validated against Micro Pulse Lidar data and compared to Moderate Resolution Imaging Spectroradiometer (MODIS) cloud mask over snow-covered areas, showing quite good correspondence to each other. Comparison of both MODIS cloud mask and presented snow mask to AATSR operational cloud mask showed that in some cases of snow surface the accuracy of AATSR operational cloud mask is questionable.
Highlights
For remote-sensing retrievals of any kind, one of the most important initial steps is to understand what we are looking at, in order to only choose those data needed for further processing
This approach has been invented for a specific task – to pick out cloud-free snow-covered regions to serve as an input for aerosol optical thickness (AOT) retrieval over snow
In order to check the performance of the presented cloud screening method over different kinds of snow surface, we processed a set of Advanced Along Track Scanning Radiometer (AATSR) scenes from both Northern and Southern hemispheres at various l3o2cations, and compared the results of operational AATSR cloud mask for nadir view, which is taken from a level 1b AATSR product, and to the Moderate Resolution Imaging Spectroradiometer (MODIS) cloud product for the same location
Summary
For remote-sensing retrievals of any kind, one of the most important initial steps is to understand what we are looking at, in order to only choose those data needed for further processing. We present a cloud-screening approach which is based on the analysis of the spectral shape of a scene reflectance and does not require time sequences of data or absolute thresholds for reflectances or brightness temperatures. This approach has been invented for a specific task – to pick out cloud-free snow-covered regions to serve as an input for aerosol optical thickness (AOT) retrieval over snow. The presented cloud screening method produces two values: “applicable for AOT retrieval over snow or determination of snow reflection (clear snow)” and “not applicable for AOT retrieval or determination of snow reflection (everything else but snow – clouds, 1 land, ocean, etc.)”
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
