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UF UNIVERSITY of FLORIDA. Understanding Soil Moisture Transport In Sandy Soils Using Multi-Frequency Microwave Observations. Pang-Wei Liu 1 , Roger De Roo 2 , Anthony England 2,3 , Jasmeet Judge 1 1. Center for Remote Sensing, Agri. and Bio. Engineering, U. of Florida

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understanding soil moisture transport in sandy soils using multi frequency microwave observations

UF

UNIVERSITYof

FLORIDA

Understanding Soil Moisture Transport In Sandy Soils Using Multi-Frequency Microwave Observations

Pang-Wei Liu1, Roger De Roo2, Anthony England2,3,

Jasmeet Judge1

1. Center for Remote Sensing, Agri. and Bio. Engineering, U. of Florida

2. Atmosphere, Oceanic, and Space Sciences, U. of Michigan

3. Electrical Engineering and Computer Science, U. of Michigan

outline
Outline
  • Introduction & Motivation
  • MicroWEX-5
  • MB Model
  • Methodology
  • Results
  • Conclusions
introduction motivation
Introduction & Motivation
  • Soil moisture (SM) is an important factor
    • In hydrology: evapotranspiration, infiltration, surface runoff, and groundwater recharge.
    • In agriculture: crop growth and yield.
  • Satellite missions for SM:
      • AMSR-E, NASA and JAXA, 2002
        • V- & H-pol passive at C-band.
        • Spatial resolution at 6.25-57km and repeat coverage in 1-2 days.
      • SMOS, ESA, Nov. 2009.
        • V- & H-pol passive at ~1.4GHz (L-band).
        • Spatial resolution at 40-50km and repeat coverage in 2-3 days
      • SMAP, NASA, Oct. 2014.
        • Active at 1.26 GHz and passive at 1.41GHz.
        • Spatial resolution of active at 1-3 km and of passive at ~40km and repeat coverage in 2-3 days.
      • Provide TB for assimilation and soil moisture retrieval.
introduction motivation1
Introduction & Motivation
  • Problem:
      • The near-surface SM is highly dynamic, particularly in sandy soils.
      • Current forward microwave algorithms typically use SM averaged over 0-5cm  may result in unrealistic TB.
  • Objectives:
      • To determine the vertical resolution of the soil moisture necessary to provide realistic TB at L-band for bare soils.
      • To utilize combined C- & L- band observations to determine the surface roughness and moisture, and the vertical resolution in the soil.
microwave water and energy balance experiments microwexs
Microwave Water and Energy Balance Experiments (MicroWEXs)
  • Series of season-long experiments conducted ata 9-acre field in NC Florida.
  • Fifth MicroWEX (MicroWEX-5): growing season of sweet corn from March 9 (DoY 68) through May 26 (DoY 146) in 2006
  • The bare soil period: from DoY 68 to 95; LAI < 0.3
  • Soil moisture and temperature values were observed every 15 minutes at the depths of 2, 4, 8, 16, 32, 64, and 120cm.
  • V- & H-pol. TB at C-band and H-pol. TB at L-band every 15 minutes.
slide6

Mesh board for soil roughness

LiDARfor soil roughness

mb model
MB Model
  • Typical Approaches
      • Radiative Transfer Equation: zero order approximation

TBsoil, p= Teff ∙ ep

        • Teff Soil temperatures at surface (TIR) and deep layer (~50cm).
        • ep= (1 - rp)  rp(εr, roughness)
        • εr (SM, soil texture) dielectric models: Dobson et al., 1996 and Mironovet al., 2009
      • Rough surface models
        • Semi-empirical model: Q-h model Wang &Choudhury, 1981 rp(εr, rmsh, f, θ).
        • Empirical model Wegmüller & Mätzler, 1999  rp(εr, rmsh, f, θ); 1-100GHz.
        • Physically-based model: IEM (Fung et al., 1992) ep(εr, rmsh, cl, f, θ);applicable for wide range of surfaces.
slide8

Comparison with observations

  • VSM0-5 from MicroWEX-5
  • Soil porosity = 0.37
  • Rms height = 0.616 cm
  • Correlation length = 8.4 cm
  • Looking angle = 50o
methodology
Methodology
  • Modifications in the MB model:
      • Soil:
          • Discrete layers with non-uniform temperature and SM.
          • Rough surface
          • Semi-infinite lower boundary
        • Sandy soils are more porous at the surface.
          • Top 1.5 cm divided into 7 layers.
          • 1.5 – 32.5 cm divided into 1cm thick layers.
          • > 32.5 cm layer thickness increases with depth
      • 1st order RTE
        • Single reflection considered at each layer interface.
        • IEM model is applied at layer 1 - rough surface
        • TB contributions from each layer combine to obtain the total TB

TB

methodology1
Methodology
  • Refractive mixing model for ε
    • Modified Mironov’s model (2010)
    • Use C-band (6.7 GHz) TB observations to estimate
      • Surface roughness  rms height and correlation length
      • Soil porosity in top 1mm
      • SM in top 1mm
    • These parameters are used with the SM observation from lower layers to estimate H-pol. TB at L-band.
results
Results
  • Estimation of rms height, correlation length, and porosity in top 1mm
  • Provide the best estimate during the dry (SM1mm = 0.01) and the wet (SM1mm= 0.29) periods
  • The SM from 0-2.5cm linearly interpolated
  • -Rms height = 0.41cm
  • -Correlation length = 8.4cm
  • -Soil porosity = 0.55
  • SM at > 2.5cm from MicroWEX-5
results1
Results
        • SM in the top 1mm b/w breaking points linearly interpolated
  • Rms height = 0.41cm
  • Correlation length = 8.4cm
  • Soil porosity = 0.55
  • Estimation of SM in top 1mm.

0.29 0.25 0.16 0.18 0.18 0.02 0.01 0.10 0.10 0.01

MicroWEX-5

Best estimation

results2
Results
  • Comparison of SM in the top 1mm with 0-5 cm SM during MicroWEX-5
  • Soil porosity: 1mm = 0.55; rest layers =0.37
  • SM profiles at wet, medium, and dry points

MicroWEX-5

results3
Results
  • Comparison of:
        • TB from MicroWEX-5
        • Case1: TB using SM 0-5 cm from MicroWEX-5.
        • Case2: TBusing best estimate of SM, porosity, and roughness in the top 1mm from C-band; SM from 1mm-2.5cm linearly interpolated; SM > 2.5cm from MicroWEX-5.
        • Case3: TBusing average of the best estimate in the top 1mm from C-band and SM at 2.5cm from MicroWEX-5; SM > 2.5 cm from MicroWEX-5; SM in top 1mm at the time of event from C-band for up to 30minutes.
results4
Results
  • Extension of methodology to the another drydown period from DoY 87.5-90.5
  • Estimation of SM in top 1mm.
        • SM in the top 1mm b/w breaking points linearly interpolated
  • Rms height = 0.41cm
  • Correlation length = 8.4cm
  • Soil porosity = 0.55

0.32 0.28 0.19 0.19 0.01 0.10 0.01

MicroWEX-5

Best estimation

results5
Results
  • Comparison of SM in the top 1mm with 0-5 cm SM during MicroWEX-5
  • Soil porosity: 1mm = 0.55; rest layers =0.37
  • SM profiles at wet, medium, and dry points

MicroWEX-5

slide17

Results

  • Comparison of:
        • TB from MicroWEX-5
        • Case1: TB using SM 0-5 cm from MicroWEX-5.
        • Case2: TBusing best estimate of SM, porosity, and roughness in the top 1mm from C-band; SM from 1mm-2.5cm linearly interpolated; SM > 2.5cm from MicroWEX-5.
        • Case3: TBusing average of the best estimate in the top 1mm from C-band and SM at 2.5cm from MicroWEX-5; SM > 2.5 cm from MicroWEX-5; SM in top 1mm at the time of event from C-band for up to 30minutes.
conclusions
Conclusions
  • SM 0-5cm is not adequate for estimating realistic TB at L-band in sandy soils, particularly during and immediately following precipitation/irrigation events.
  • TB at C-band may be used to derive soil surface characteristics such as roughness, porosity, and SM.
  • TB at L-band may be obtained using the derived properties and the observations at 2cm.
  • Future work: Extending/generalizing the methodology for larger applicability.
acknowledgment
Acknowledgment
  • NASA Terrestrial Hydrology Program (NASA-THP-NNX09AK29G)
  • MicroWEX-5 was supported by the NSF Earth Science Division (EAR-0337277) and the NASA New Investigator Program (NASA-NIP-00050655).
slide22

The VSM at 1mm layer was set at 1% in dry period.

- rmsh=0.616cm, cl=8.4cm

- soil porosity = 0.5

slide23

The VSM at 1mm layer was set at 29% in the wet period.

-rmsh=0.41cm, cl=8.4cm

-Porosity = 0.5

results6
Results
  • Comparison of radiative emission models.

Overall, 484 pairs of soil moisture and temperature profiles were applied.

The average difference is within 3K at L-band.

1st order model was applied for further work.