1. STAR-Light: Enabling a New Vision for Land Surface Hydrology in the Arctic A. W. England and Roger De Roo Atmospheric, Oceanic, and Space Sciences Electrical Engineering and Computer Science The University of Michigan Abstract STAR-Light, a 1.4 GHz radiometer for use on light aircraft, is an enabling instrument for monitoring thickness and water content of the active layer throughout the circumpolar Arctic. Our underlying vision is that the active layer can be modeled with a Soil-Vegetation-Atmosphere Transfer (SVAT) model that is forced by available data on weather and downwelling radiation. Through near- daily assimilation of satellite observations of microwave brightness at a frequency that is sensitive to liquid water in the upper few centimeters of soil, these SVAT models will maintain reliable spatial estimates of the thickness and water content of the active layer. Key for this vision are accurate SVAT models for Arctic terrains, an airborne radiometer for the extensive field observations necessary to calibrate these models, and a satellite radiometer to provide near-daily observations. SVAT/Radiobrightness models for Arctic tundra are in the early stages of development. The hydrology community has converged upon 1.4 GHz brightness as the most effective observation for sensing soil moisture, and the European Space Agency is completing a preliminary study of a 1.4 GHz Soil Moisture Ocean Salinity (SMOS) satellite mission for later this decade. STAR-Light is an NSF-funded, airborne instrument for SVAT model calibration in the Arctic beginning in 2004. We will describe our progress with the STAR-Light development, and describe how others can participate in this research. Background 1)‘Stored water’ is an important unmeasured parameter limiting the predictive skills of continental weather and climate models  Desire to estimate stored water, on a near-daily basis, globally, and at ~10 km resolution 2)Climate models predict early & significant warming in the Arctic Observed warming of permafrost Concern about transition of Arctic from carbon sink to carbon source  Desire to monitor evolution of active layer throughout Arctic Seasonal duration Water content Access to Arctic tundra is limited in summer  Desire for supporting land surface hydrology observations from airborne and satellite sensors Operational Strategy for Estimating Stored Water Objective Design and fabricate a reliable L-band imaging radiometer for use on light aircraft in Arctic land-surface hydrology Strategy Use Synthetic Thinned Aperture Radiometer (STAR) technology for compactness Use Direct Sampling Digital Receivers (DSDR) for reliability and compactness Use Digital Signal Processing technology for uniform band definition These technologies move complexity from analog domain to digital domain and achieve compactness, reliability, and flexibility Development/calibration of SVAT/radiobrightness models of Arctic tundra require observations from thawing in spring to freezing in fall NASA radiometers used for hydrology are designed to fly on large, 4-engine, turboprop aircraft like the C-130 and P-3 High operations costs and scheduling conflicts prohibit use of these aircraft in field campaigns of more than a few weeks Operations costs of STAR-Light will be < 5% those of NASA systems and the aircraft will be dedicated to STAR-Light enabling season-long field campaigns A 1.4 GHz radiometer on a light aircraft would greatly facilitate remote sensing hydrology in the Arctic STAR-Light Control Module STAR-Light Sensor Module Observational Scales and Deployment Timeline Estimates of stored water from SVAT models running in open loop (blue arrows) diverge from reality over time (due to imperfect weather data, poor estimates of runoff, etc.) Closed loop (yellow arrows) estimates of stored water use remotely sensed radiobrightness data to quantify surface soil moisture and thereby correct model and data imperfections over time. Calibrating SVAT Models with Season-long Observations This work is supported by NSF grant OPP-0085176 from the Office of Polar Programs SVAT/Radiobrightness ModelFrequencies (GHz)StatusAvailabilitySponsor Prairie Grasslands 19, 37, 85CalibratedNowNASA Hydrology Row Crops (corn)1.4Calibratedmid 2002NASA Hydrology Tussock Tundra 19, 37, 85PreliminaryNowNSF LAII Meadow with Snowpack1.4, 6.9, 19, 37Funded2004NASA CLPX & GWEC Tussock Tundra1.4, 6.9, 19, 37Funded2005NASA GWEC 1 m1 km1000km TMRS ‘04 STAR-Light ‘04 SMOS scheduled launch ‘05 The University of Michigan European Space Agency SVAT & Radiobrightness Models Weather & Downwelling Radiation Data Temperature & Moisture Profile Prediction T b Prediction T b Data Refinements Airborne L-band Radiometer and Truck Multi-frequency Radiometers Temperature & Moisture Profile Data Refinements Micromet Tower and buried sensors We are developing and will calibrate the SVAT/Radiobrightness model for tussock tundra near Toolik Lake. We seek collaborators to: Develop & calibrate SVAT/Radiobrightness models for other Arctic terrains Develop & calibrate 2-D land-surface hydrology/radiobrightness models Field test models in relevant Arctic terrains Atmospheric Model Weather & Downwelling Radiation Temperature & Moisture Profiles T b (model) T b (observed) Assimilate T b (observed) - T b (model) Satellite L-band Radiometer (University of Michigan research area) Radiobrightness Model (University of Michigan research area) Stored Water Estimate Calibrated Soil-Vegetation-Atmosphere-Transfer (SVAT) Model (University of Michigan research area)