fr4.l10.3: how does dew affect l-band backscatter? analysis of pals data at the iowa validation site...

Brian Hornbuckle,Tracy Rowlandson, Eric Russell

Amy Kaleita, Sally Logsdon,Anton Kruger, Simon Yueh,

and Roger De Roo

How Does Dew Affect L-band Backscatter?Analysis of PALS Data at the Iowa Validation Site

and Implications for SMAP

IGARSS 2010, Honolulu, Hawaii

Hornbuckle et al., Dew and L-band Backscatter, Implications for SMAP?

European Space AgencySoil Moisture and Ocean Salinity (SMOS) in orbit.

L-band brightness temperature.

Spatial resolution: 40 km.

Global-scale measurements of soil moisture at L-band...

NASA Soil Moisture Active-Passive (SMAP)scheduled launch in 2014/2015.

L-band brightness temperature and backscatter.

Spatial resolution: 10 km.

Hornbuckle et al., Dew and L-band Backscatter, Implications for SMAP?

Are changes in backscatter over short periods of timeonly due to changes in soil moisture?

Hornbuckle et al., Dew and L-band Backscatter, Implications for SMAP?

dew frequencyin soybean

SMOS/SMAP overpass

50%

Hornbuckle et al., Dew and L-band Backscatter, Implications for SMAP?

PALS visit to Iowa Validation SiteSMAPVEX08

September 23-25, 2008

Hornbuckle et al., Dew and L-band Backscatter, Implications for SMAP?

Iowa Validation Site

eddy-correlation flux towersfour-component radiation

soil moisture and temperatureprecipitation

Hornbuckle et al., Dew and L-band Backscatter, Implications for SMAP?

Flights over Iowa Validation Site.

IVSB A

N

footprint size @ 3000 ft AGL

Hypothesis: dew affects the brightness temperatureand radar backscatter.

Timing: PALS flies to catch maximum dew and to observe dew dry-off.

Hornbuckle et al., Dew and L-band Backscatter, Implications for SMAP?

Soybean plants at IVS on 9/25/2008.

Hornbuckle et al., Dew and L-band Backscatter, Implications for SMAP?

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

Hornbuckle et al., Dew and L-band Backscatter, Implications for SMAP?

optical depth, Np

Hornbuckle et al., 2010, under review, WRR.

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 .

Hornbuckle et al., Dew and L-band Backscatter, Implications for SMAP?

1 2direct canopybackscatter

canopy-groundor ground-canopy

bistatic scatter

ground-canopy-ground

backscatter

soil backscatterattenuatedby canopy

3 4

How will dew affect L-band backscatter?

Hornbuckle et al., Dew and L-band Backscatter, Implications for SMAP?

How will dew affect L-band backscatter?

1 2direct canopybackscatter

canopy-groundor ground-canopy

bistatic scatter

ground-canopy-ground

backscatter

soil backscatterattenuatedby canopy

3 4

Hypothesis: Dew will decrease L-band backscatter.

Hornbuckle et al., Dew and L-band Backscatter, Implications for SMAP?

Hornbuckle et al., Dew and L-band Backscatter, Implications for SMAP?

0.6 dB

1.3 dB

0.7 dB

Hornbuckle et al., Dew and L-band Backscatter, Implications for SMAP?

Can we explain the effect of dew on L-band backscatter?

2 4

4

2 4

Hornbuckle et al., Dew and L-band Backscatter, Implications for SMAP?

0.6 dB

1.3 dB

0.7 dB

0

2 4

2 4

Hornbuckle et al., Dew and L-band Backscatter, Implications for SMAP?

0.6 dB

1.3 dB

0.7 dB Dew should have the greatest affect

on , but it does not.

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 m3 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 backscatterbut incorrectly predicts the relative changes.

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 m3 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 backscatterbut incorrectly predicts the relative changes.