Land and Cryosphere Applications for Aquarius Data
On the use of observations from the Aquarius/SAC-D mission to study the cryosphere
Contact author: Emmanuel Dinnat, <firstname.lastname@example.org>
Emmanuel Dinnat, Chapman University/NASA GSFC
Ludovic Brucker, NASA-GSFC
Passive and active microwave observations at 1.413 GHz (L-band) from the Aquarius/SAC-D mission offer new capabilities to study and to monitor the cryosphere. To offer an easy use of the Aquarius data over the polar regions, and to move forward our understanding of the L-band observations of ice sheet, sea ice, and frozen soil, three weekly polar-gridded products were developed. Aquarius data recorded at northern and southern latitudes higher than 50º were averaged and gridded into weekly products of Brightness Temperature (TB), Normalized Radar Cross Section (NRCS), and Sea Surface Salinity (SSS). These products are routinely distributed by the U.S. National Snow and Ice Data Center (NSIDC); see http://nsidc.org/data/aquarius/data-sets.html#L3-weekly-polar-grid.
Due to the low microwave dielectric loss of dry snow and ice, L-band radiation has a large penetration depth. The energy emitted at depth, up to hundreds of meters, propagates from the ice and snow toward the surface with little attenuation. Aquarius’ excellent radiometric sensitivity (~0.2 K per footprint observation over snow-covered surfaces) makes it possible to study in details observations over the cryosphere.
The objective of this talk is to present the high-latitude products and to summarize their recent applications over the cryosphere. The effect of the 2012 summer melt event at Summit, Greenland created sudden TB drops, larger than 15 and 20 K at vertical and horizontal polarization, respectively. These TB drops result from the snow surface refreeze. After the melt/refreeze cycle, the TB level remained lower than before the event (by about 5 K at horizontal polarization), revealing the significant impact that a refrozen snow layer can have on the L-band TB, and thus on the monitoring of long-term snow accumulation.
We will also emphasize the impact of snow surface changes on the Aquarius L-band TB observations at Dome C (75S, 123E). Aquarius TB at Dome C is characterized by large summer-time variations, larger than 2 K at horizontal polarization, whereas no melt occurs there. Results show that these TB variations are correlated to changes in the snow properties at the surface, which is observed by a surface-based near-infrared camera taking picture of the surface every hour. Therefore, evolutions of the snow properties near the surface, that usually change rapidly and irregularly, need to be precisely quantified to use the Antarctic Plateau as a calibration/inter-calibration target.
Finally, we will show that the scatterometer observations are sensitive to the anisotropy of the Antarctic ice sheet. Specifically, the difference between observations collected during ascending and descending orbits can be correlated with ice drainage basin. To analyze this particularity, a Pauli decomposition was considered.