New Projects: Collaborators Sought NSF OPP Instrumentation Project: STAR-Light – a 1.4 GHz aperture synthesis radiometer for use on light aircraft in arctic land-surface hydrology PI – England NASA GEWEC Project: The subsurface geothermal climate signal in the context of LSP/Radiobrightness model-based estimates of land- atmosphere energy and moisture fluxes for regions of the circumpolar Arctic Co-PI’s – England and Pollack

Background 1) Climate models predict early & significant warming in the Arctic –Transition of Arctic tundra from carbon sink to carbon source 2) Geothermal climate signal is used to infer climate trends –Unclear how surface processes influence the geothermal gradient 3)Desire to use satellite microwave radiometry to monitor annual duration and water content of active layer REBEX-3 Toolik Lake Alaska

Strategy for Monitoring Arctic Tundra Atmospheric Model Weather & downwelling irradiance Land Surface Process Model Temperature & Moisture Profiles Radiobrightness Model Satellite L-band Radiometer Tb (model) Tb(observed) Assimilate Tb(observed) - Tb(model)

1.4 GHz Radiometer on Light Aircraft Would Facilitate Remote Sensing Hydrology in Arctic Calibration of Arctic LSP/R model requires data from thawing in spring to freezing in fall Arctic is inaccessible to grounds surveys in summer NASA radiometers fly on 4-engine, turboprop aircraft like the C-130 and P-3 Operations costs of these aircraft are prohibitive Operations costs of STAR-Light will be < 5% those of NASA systems enabling season-long field campaigns

STAR-Light Objective: Build a reliable L-band imaging radiometer for use on light aircraft in Arctic land-surface hydrology Strategy: STAR technology Direct Sampling Digital Receivers (DSDR) Band definition filters in digital domain

Requirements for STAR-Light 1.4 GHz, 10-element, circularly polarized, aperture synthesis radiometer Angular resolution: 90% beam efficiency NE  T < 0.1 K desired, < 0.5 K required Calibration: < 2 K desired, < 3 K required Linear dynamic range 5 K < Tb < 300 K Ambient operating range -30 o C < T o < +30 o Across-track scan to ±35 o Along-track scan + 20 o / -50 o Operation on a Super Cub-class aircraft for extended periods in the Arctic Flight Direction m STAR-Light element configuration

Future Satellite System Sketch of the ESA Soil Moisture Ocean Salinity (SMOS) satellite

Objectives of our GEWEC Project Develop a tundra LSP/R model that will credibly generate the downward propagating temperature signal used to infer past climate Quantify constraints placed upon the land-atmosphere energy and moisture fluxes by the geothermal climate signal Quantify expected errors in estimated land-atmosphere energy and moisture fluxes obtained from the tundra LSP/R model and assimilated AMSR or SMOS data

Principal Tasks of our GEWEC Project Develop a physically plausible LSP/R model for tussock tundra Calibrate the model with data from a REBEX-style field experiment near Toolik Lake, Alaska, during summer of 2003 Establish the open-loop sensitivity of model-generated geothermal signals to plausible ranges of land-atmosphere energy and moisture fluxes Compare modeled geothermal climate signals with borehole temperature data in permafrost from the Alaskan North Slope