How Dew Affects L-band Backscatter and SMAP Estimates
1. How Does Dew Affect L-band Backscatter?
Analysis of PALS Data at the Iowa Validation Site
and Implications for SMAP
Brian Hornbuckle,
Tracy Rowlandson, Eric Russell
Amy Kaleita, Sally Logsdon,
Anton Kruger, Simon Yueh,
and Roger De Roo
IGARSS 2010, Honolulu, Hawaii
2. Hornbuckle et al., Dew and L-band Backscatter, Implications for SMAP?
Global-scale measurements of soil moisture at L-band...
European Space Agency
Soil Moisture and Ocean Salinity (SMOS) in orbit.
L-band brightness temperature.
Spatial resolution: 40 km.
NASA Soil Moisture Active-Passive (SMAP)
scheduled launch in 2014/2015.
L-band brightness temperature and backscatter.
Spatial resolution: 10 km.
3. Hornbuckle et al., Dew and L-band Backscatter, Implications for SMAP?
Are changes in backscatter over short periods of time
only due to changes in soil moisture?
4. Hornbuckle et al., Dew and L-band Backscatter, Implications for SMAP?
dew frequency
in soybean
50%
SMOS/SMAP overpass
5. Hornbuckle et al., Dew and L-band Backscatter, Implications for SMAP?
PALS visit to Iowa Validation Site
SMAPVEX08
September 23-25, 2008
6. Hornbuckle et al., Dew and L-band Backscatter, Implications for SMAP?
Iowa Validation Site
eddy-correlation flux towers soil moisture and temperature
four-component radiation precipitation
7. Hornbuckle et al., Dew and L-band Backscatter, Implications for SMAP?
Hypothesis: dew affects
N the brightness temperature
and radar backscatter.
Flights over Iowa Validation Site.
IVS footprint size @ 3000 ft AGL
B A
Timing: PALS flies to catch maximum dew
and to observe dew dry-off.
8. Hornbuckle et al., Dew and L-band Backscatter, Implications for SMAP?
Soybean plants at IVS on 9/25/2008.
10. Hornbuckle et al., Dew and L-band Backscatter, Implications for SMAP?
Can we explain the effect of dew on L-band brightness?
optical depth, Np canopy water, kg m-2
11. Hornbuckle et al., Dew and L-band Backscatter, Implications for SMAP?
optical depth, Np
Hornbuckle et al., 2010, under review, WRR.
12. Hornbuckle et al., Dew and L-band Backscatter, Implications for SMAP?
optical depth, Np
Hornbuckle et al., 2010, under review, WRR.
Dew is twice as important as .
13. Hornbuckle et al., Dew and L-band Backscatter, Implications for SMAP?
How will dew affect L-band backscatter?
1 2 3 4
direct canopy canopy-ground ground- soil backscatter
backscatter or ground-canopy canopy- attenuated
bistatic scatter ground by canopy
backscatter
14. Hornbuckle et al., Dew and L-band Backscatter, Implications for SMAP?
How will dew affect L-band backscatter?
1 2 3 4
direct canopy canopy-ground ground- soil backscatter
backscatter or ground-canopy canopy- attenuated
bistatic scatter ground by canopy
backscatter
Hypothesis: Dew will decrease L-band backscatter.
16. Hornbuckle et al., Dew and L-band Backscatter, Implications for SMAP?
1.3 dB
0.6 dB
0.7 dB
17. Hornbuckle et al., Dew and L-band Backscatter, Implications for SMAP?
Can we explain the effect of dew on L-band backscatter?
2 4
2 4
18. Hornbuckle et al., Dew and L-band Backscatter, Implications for SMAP?
1.3 dB 2 4
0.6 dB
0.7 dB
19. Hornbuckle et al., Dew and L-band Backscatter, Implications for SMAP?
1.3 dB 2 4
0.6 dB
0.7 dB Dew should have the greatest affect
on , but it does not.
20. Hornbuckle et al., Dew and L-band Backscatter, Implications for SMAP?
Conclusions
A modest dew increased L-band backscatter from soybean (new science).
increased by 0.6 dB. Soil moisture sensitivity is ~ 0.2 dB per m 3 m-3 .
Dew affects and more than for a soybean canopy.
Sub-daily change in canopy water caused by dew could produce
incorrect SMAP change-detection soil moisture estimates.
A semi-empirical soybean model predicts an increase in L-band backscatter
but incorrectly predicts the relative changes.
21. Hornbuckle et al., Dew and L-band Backscatter, Implications for SMAP?
Conclusions
A modest dew increased L-band backscatter from soybean (new science).
increased by 0.6 dB. Soil moisture sensitivity is ~ 0.2 dB per m 3 m-3 .
Dew affects and more than for a soybean canopy.
Sub-daily change in canopy water caused by dew could produce
incorrect SMAP change-detection soil moisture estimates.
A semi-empirical soybean model predicts an increase in L-band backscatter
but incorrectly predicts the relative changes.
