Satellite Microwave Radiometry: Current and Future Products Rogre De Roo and Tony England Atmospheric, Oceanic, and Space Sciences

Outline Principles of Microwave Radiometry Observables History of spaceborne missions Future missions and opportunities

Radar Radiometry TxRx 1.Long wavelengths (3mm to 30cm) don’t scatter off of objects the size of cloud droplets -- microwaves see through clouds 2.Source of power is independent of the sun -- microwaves see at night and day Very high spatial resolution Power hungry: expensive Sensitive to geometry of water Poor spatial resolution Low power requirements Insensitive to geometry of water What’s so great about Microwave Remote Sensing?

1 GHz 0.3 m 1 THz 0.3 mm 1 PHz 0.3 um 8000K white hot the Sun frequency wavelength 3K outer space 30K 300K room temp 3000K red hot Microwave Radiometry & Planck Radiation

Microwave Characteristics of the Atmosphere from LeVine, Wilheit, Murphy and Swift, 1989

Water molecules have large electric dipole, unlike rest of nature An interface w/ high contrast of index of refraction leads to reflection Dry soils appear warm, while wet soils appear cold, at the same temp. H - O + H Space 2.7K Dry Soil ~300K Sensor Space 2.7K Wet Soil ~300K Sensor Liquid water molecules will orient itself with passing electromagnetic waves,slowing the wave down The molecule can keep up with the wave until ~9 GHz (index of refraction: n = 9 at 1 GHz, but n = 2 at 100 GHz) Microwave Brightness and Moisture

Freeze/ Thaw Example: Liquid water n=9 Frozen water (ice) n=1.77

Strategy for Estimating Stored Water Atmospheric Model Weather & downwelling radiance SVAT Model Temperature & Moisture Profiles Radiobrightness Model Satellite L-band Radiometer Tb (model) Tb(observed) Assimilate Tb(observed) - Tb(model) Microwave Geophysics Group calibrating models in AK, 1995

Products by frequency from LeVine, Wilheit, Murphy and Swift, 1989 Also: -Sea surface salinity at 1.4GHz -Vegetation moisture content at 1.4 and 6 GHz -Vegetation temperature at 18 – 90 GHz

Future Systems and Opportunities: 1.4GHz (21cm) SMOS (by ESA) in 2007: a very ambitious electronically steered array to collect soil moisture at 50 km and sea surface salinity at 300 km Aquarius (by NASA) in 2010: relatively traditional design optimized for sea surface salinity observations. HYDROS (by NASA) in 2012: relatively traditional design optimized for soil moisture measurements. Soil moisture measurements have obvious hydrological value to GLACEO Sea surface salinity…

Sea Surface Salinity ??? Great Lakes are a natural calibration target for a SSS mission: –Body of water with known salinity (none!) –Large extent for low spatial resolution observations –Conveniently located close to many scientists However, spatial resolution for SSS is so poor, even Lake Superior may not be big enough. Accurate meteorological and ecological data on the lakes and nearby lands will add utility to use of the lakes as calibration / validation target.