AVHRR data at high latitudes

Accurate real-time navigation of AVHRR data at high latitudes

It is a well known problem that without any kind of special post-processing locally received high-resolution meteorological satellite data may have navigational errors causing the footprints to be displaced several kilometres. These errors fluctuates in time (significant changes from day to day is normal) and may significantly degrade the output of geophysical satellite retrievals (see the figure). The navigational errors are due mainly to an uncertainty in the satellite attitude (its orientation) and the satellite position and velocity.
Norska havet och Lofoten                                               Norska havet och Lofoten
Nowcasting SAF Cloud Mask (see http://www.smhi.se/saf/) assuming nominal attitude (left) and with navigation adjustment using ANA (right) over the Norwegian Sea and Lofoten (Norway) April 8, 2001, 11:05 UTC, NOAA16. Blue and green are cloud free sea and land respectively, and white is either snow cover or sea ice. Clouds are either grey (cloud contaminated pixels) or orange (cloud filled pixels). Notice that the poor navigation causes an artificial increase in cloud cover along the coast, and that snow cover on land may be taken as sea-ice.

This project aims at improving the operational geolocation (navigation) of the Advanced Very High Resolution Radiometer (AVHRR) data of the Polar orbiting NOAA satellites received at SMHI, and make it possible to provide better and more advanced derived high latitude products to the Swedish user community. We think this will especially concern satellite derived cloud climatologies and snow cover mapping.

At CMS Météo-France, an advanced Automatic Navigation Adjustment (ANA) technique developed by Brunel and Marsouin (2000) has been used operationally since 1990 to provide highly accurate geo-located AVHRR data. ANA combines a physical image deformation model and automatic adjustment on coastal landmarks. The ANA software has recently been made compatible with the EUMETSAT ATOVS and AVHRR processing package, AAPP, which is becoming a standard also for processing AVHRR data, and thereby ANA is for the first time available outside Météo-France. However, ANA has up till now never been tested at high latitude conditions.

In this project we will evaluate ANA at high latitudes, and further develop the algorithm specifically to be more efficient during night-time.

Contact person: Adam Dybbroe, SMHI. E-mail: adam.dybbroe@smhi.se

Senast uppdaterad: 28 maj 2009