Common References for Inter Comparison of L-Band Brightness Temperatures Satellite Acquisitions.

Abstract:

The SMOS mission, in orbit since November 2009, has been the first spatial instrument observing the earth at L-Band since the Skylab experiment in 1977. Since then, it has been joined by Aquarius in June 2011, and will be joined by SMAP in October 2014.

Within these 4 years, earth observation at L-band has gone from historical curiosity to highly repetitive constellation.

Still, since all these instruments do not share the same technology and even principle of acquisitions, direct comparison and synergistic use of their measurements is not straightforward.

The objective of this paper is to propose a method to make them inter-comparable, down to a common reference. The proposed method uses SMOS as a transfer radiometer.

This method can be applied over different types of surfaces:

• making use of a stable target to assess the consistency and stability of both data sets. This is done over the area surrounding Dome Concordia in Antarctica. After careful selection and filtering, statistics of the comparison are retrieved along with long term trends in both data sets.

• Once every so often, satellites overpass the same area within a very short time period. Due to different inclinations these alignments occur essentially along the equator, but over different surfaces, giving access to wide dynamic range in brightness temperature. These collocation will be happening at about the same frequency for Aquarius and SMAP.

After careful selection, SMOS measurements is used in an innovative way - taking advantage of it accessibility to wide areas with a large range of incidence angles - to make it directly comparable to other instruments. Accounting for instrument characteristics such as real antenna patterns is also done at this step. This presentation will completely describe the method, along with examples of results when applied to compare SMOS and Aquarius measurement. Although these methods have already been presented and demonstrated, this presentation will include demonstration of use for the SMAP mission, potential benefits to all three missions. Building blocks of of a long term brightness temperature record, spanning the lifetime of the three missions will also be presented.