Improving the Cloud Mask For MERIS/ENVISAT Imagery Received Over Canada
Abstract
Since the beginning of 2008 two new receiving stations have started a regular reception of Full Resolution Full Swath (FRFS) data from MERIS/ENVISAT over the North America region. They are operated by the Canada Centre for Remote Sensing (CCRS) and located in Gatineau, QC (45.5degN; 75.7degW) and Prince Albert, SK (53.2degN; 105.7degW). The FRFS MERIS imagery consists of 15 spectral bands covering spectral range from 412nm to 900nm with 260m x 290m spatial resolution. The standard MERIS data processing system has been used to generate MERIS level 1 (L1) and level 2 (L2) products. An analysis of the standard MERIS products generated from data received by two new stations revealed that produced cloud mask is not very reliable. The high quality cloud mask is required for many applications, such as aerosol retrievals, albedo mapping, vegetation property retrievals, snow/ice cover extent mapping etc. The generated cloud mask is especially unreliable during the cold season over snow and ice covered surfaces. To address this issue, we developed a new cloud screening algorithm, that utilizes some special features of MERIS imagery to improve separation between clouds and snow/ice covered areas. New spectral indices were introduced to better utilize available spectral features of MERIS imagery in the atmospheric transparent bands as well as oxygen (channel 11) and water vapour (channel 15) absorption bands. New cloud detection algorithm also introduces an empirical parameter called cloud contamination rating that indicates the degree of cloud contamination and can be useful for generating clear sky-composites, when decision has to be made about “the best pixel” selection. Testing showed that reliability of cloud detection for complex scenes with presence of bright surface types such as snow and ice has been significantly improved. Improvement may reach 90% or more relative to a standard product for some scenes and regions.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFM.A13F0289T
- Keywords:
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- 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0305 ATMOSPHERIC COMPOSITION AND STRUCTURE / Aerosols and particles;
- 0321 ATMOSPHERIC COMPOSITION AND STRUCTURE / Cloud/radiation interaction;
- 0480 BIOGEOSCIENCES / Remote sensing