STAR-Light: Enabling a New Vision for Land Surface Hydrology in the ArcticA. W. England and Roger De Roo

Atmospheric, Oceanic, and Space SciencesElectrical 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 Model Frequencies (GHz) Status Availability SponsorPrairie Grasslands 19, 37, 85 Calibrated Now NASA HydrologyRow Crops (corn) 1.4 Calibrated mid 2002 NASA HydrologyTussock Tundra 19, 37, 85 Preliminary Now NSF LAIIMeadow with Snowpack 1.4, 6.9, 19, 37 Funded 2004 NASA CLPX & GWECTussock Tundra 1.4, 6.9, 19, 37 Funded 2005 NASA GWEC

1 m 1 km 1000km

TMRS ‘04 STAR-Light ‘04 SMOS scheduled launch ‘05

The University of MichiganThe University of Michigan

European Space Agency

SVAT & Radiobrightness Models

Weather & Downwelling RadiationData

Temperature & Moisture Profile Prediction

Tb Prediction

Tb DataRefinements

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 Tb (model)

Tb (observed)

Assimilate Tb(observed) - Tb(model)

Satellite L-band Radiometer(University of Michigan research area)

Radiobrightness Model(University of Michigan research area)Stored Water Estimate

CalibratedSoil-Vegetation-Atmosphere-Transfer (SVAT) Model

(University of Michigan research area)