3. Sea surface temperature from AATSR

Aim and objectives

This lesson introduces you to the ENVISAT Advanced Along-Track scanning Radiometer (AATSR), and shows how data from this instrument can be used to map fine scale sea surface temperature patterns in the western Mediterranean Sea. At the end of the lesson you should be able to:

• Understand the unique measurement capability and main features of the ENVISAT AATSR instrument.
• Identify the main features of the AATSR ATS_TOA_1P Gridded Brightness Temperature and Reflectance (GBTR) data product.
• Characterise the general sea surface temperature (SST) patterns in the Western Mediterranean Sea using AATSR data.
• Understand the basic principles of cloud flagging using AATSR data at night
• Understand multi-spectral and multi-view atmospheric correction techniques and the difference between brightness temperature image data sets and sea surface temperature maps
• Measure and describe meso-scale and fine scale thermal features of the Balearic Basin, Gulf of Lions and Algerian Basin of the Mediterranean Sea.

Try to refer back to these objectives as you work therough this lesson. The lesson should take you about 2 -3 hours to complete.

Lesson content

1. Becoming familiar with AATSR GBTR data
   opening and examining ATS_TOA_1*.N1 file structure, and loading individual images.
2. Surface wind in the study area
   investigating surface wind fields using Met Office model output
3. Masking cloud and land pixels
   using L1 flags to create masks and assigning Null values to masked pixels
4. Look-angle differences in brightness temperature
   investigating differences between the forward and nadir view data sets
5. 6-channel SST retrieval
   computing sea surface skin temperature from 6 AATSR GBTR channels.
6. Summary and conclusions

Images used in this lesson

• ATS_TOA_1COLRA20020727_~.N1 Two level 1 images from the Mediterranean between Algeria and Spain showing top of atmosphere (TOA) brightness temperature measured by the AATSR sensor onboard ESA's Envisat satellite on July 27th, 2002.
• cdWE020727wind_*.dat Two images giving the wind field in the study area on July 27th, 2002. The images are part of the output of the UK Met Office European wave model. One image represents the wind speed in m s^-1; the other wind direction given in degrees (0-360°) where 0° represents winds from the North, 90° represents wind from the East, 180° wind from the South and 270° winds from the West.