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Soil Moisture: Questions and Requirements

Soil Moisture: Questions and Requirements. Jeffrey Walker Dept of Civil and Env Engg The University of Melbourne, Australia http://www.civenv.unimelb.edu.au/~jwalker Jetse Kalma School of Civil, Surveying and Env Engg The University of Newcastle, Australia. Importance of Soil Moisture.

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Soil Moisture: Questions and Requirements

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  1. Soil Moisture: Questions and Requirements Jeffrey WalkerDept of Civil and Env Engg The University of Melbourne, Australia http://www.civenv.unimelb.edu.au/~jwalker Jetse Kalma School of Civil, Surveying and Env Engg The University of Newcastle, Australia

  2. Importance of Soil Moisture • Early warning systems • Flood prediction – infiltration • Socio-economic activities • Agriculture – yield forecasting, management (pesticides etc), sediment transport • Water management – irrigation • Policy planning and decision making • Drought relief • Global change • Military – trafficability • Weather and climate • Evapotranspiration – latent and sensible heat

  3. The Situation R e m o t e S e n s i n g S a t e l l i t e L o g g e r S o i l M o i s t u r e M o d e l f  (z) [ q , D ( ) , ( ) ]      s Stream Gauge S o i l M o i s t u r e S e n s o r s

  4. The Problem With LSMs • Same forcing and initial conditions but different predictions of soil moisture! Houser et al., GEWEX NEWS 2001

  5. 6.6 GHz 10.7 GHz Soil Moisture Coverage: Veg (Mean PR) Njoku, personal communication (JPL)

  6. Basis of Soil Moisture Sensing • Contrast of soil (2) and water (80) dielectric properties • For smooth bare soil: • For smooth vegetated soil: where Tveg is the physical temperature of the soil (K) Tveg is the physical temperature of the vegetation (K) vegis the transmissivity of the vegetation layer  is the single scattering albedo of the vegetation ep is the smooth soil emissivity at polarisation p

  7. where  is the sensor look angle r is the dielectric constant relative to free space where  is the soil moisture where veg is the vegetation moisture b is an empirical parameter (from graph)

  8. Problem … • Assuming you know soil properties, assume soil roughness, vegetation albedo and that Tsoil=Tveg, unknowns are: • soil moisture content • soil temperature • vegetation water content/optical depth 1. estimate soil temperature from thermal infrared data + v and h pol microwave 2. Use multi-incidence angle data for single ground pixel

  9. Questions • Spatial, temporal and accuracy requirements for satellite missions • Development and validation of passive microwave algorithms – AMSR-E/SMOS/ Hydros – scaling, multiangle, etc • Downscaling of low resolution passive microwave soil moisture measurements using high resolution visible/thermal data and/or radar (ie Hydros) • Retrieval and validation of derived root zone soil moisture from the assimilation of near-surface measurements

  10. Mission Requirements Needs to be explored with real data! Walker and Houser

  11. Algorithm Validation & Development Algorithms need further development! Walker et al.

  12. Downscaling: Thermal/NDVI Data Approach needs to be validated! Hemakumara et al.

  13. 36km radiometer inverse 3km radar inverse 3km retrieval Downscaling: Active/Passive Error in 3km soil moisture content Needs to be tested with real data! Zhan et al.

  14. Root Zone Soil Moisture NDVI Data Needs to be validated! Walker et al.

  15. Ground Requirements • Long-term monitoring of soil moisture profiles and associated meteorological data • for modelling and evaluation of root zone soil moisture • Extensive ground-based measurement of near-surface soil moisture and soil temperature across individual farms at scales of 2.5m to 150m spacing during airborne monitoring campaigns • for aircraft validation and scaling, algorithm development, downscaling and mission requirements • Continuous near-surface soil moisture, soil temperature, and thermal infrared logging at focus farms • for relating air/ground measurements

  16. Air Requirements • Fly with passive microwave, thermal and NDVI scanner • would also like lidar scan and digital photography (once) • Air measurements coinciding with ground measurements, as early in the morning as possible • soil and veg temperatures are more closely aligned • more uniform soil temperature profile • Hydros/SMOS have 6am/pm overpass; AMSR-E has 10am/pm overpass • Fly at a range of altitudes to achieve a range of ground resolutions • provides data for scaling, root-zone, algorithm development/validation and mission requirements • 50m at 500ft (farms) to 1km at 10,000ft (regions) for microwave • 1m at 500ft to 20m at 10,000ft for thermal & NDVI • Fly farms with instrument in multiangle configuration • Provides data for SMOS algorithm development

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