Remotely sensed ground surface temperature variations over Arctic during summer and winter (under snow cover) periods

Abstract:

Projected future warming is particularly strong in northern high latitudes. Permafrost present in those areas contains high quantities of “frozen carbon” that could be released in the atmosphere. This communication will present different improved approaches to monitor the land-surface temperature (LST) variations in summer (without snow) and in winter (under snow cover), using microwave brightness temperatures.

 For the summer period, the method combines 37 GHz passive microwave and thermal infrared data to estimate LST during summer snow-free periods calibrated at a pixel-based scale, leading to a new LST dataset provided at 25 km scale and at an hourly time step during the ten-year analysis period (2000–2011). This product was locally evaluated at five experimental sites of the EU-PAGE21 project against air temperature measurements and meteorological model reanalysis, and compared to the MODIS LST product at both local and circumpolar scale. The results giving a mean RMSE of the order of 2.2 K demonstrate the usefulness of the microwave product, which is unaffected by clouds as opposed to thermal infrared products and offers a better resolution compared to model reanalysis.

The snow impact on ground temperature, due to its insulation properties modified by the climate changes, must also be monitored. For the winter period, we use satellite data (MODIS “LST” and passive microwave AMSR-E “Tb”) assimilated in a climate land surface scheme (CLASS) driven by reanalysis meteorological data and coupled with a radiative transfer model (HUT) in order to generate a daily Tb corresponding the simulated soil and snow conditions. The land surface scheme is adjusted to minimize the simulated Tbs against the measured Tbs. We show that the retrieved simulated ground-temperatures under the simulated modified snow cover is improved by up to 2 to 4 K when using satellite data compared to the simulated ground temperatures using the model (alone) without constraint.