GPS-soil moisture measurements at SMAP ISST

xenon.colorado.edu/reflections/GPS_reflections/PBO_H2O.html

Eric Small, Geological Sciences, CU Boulder eric.small@colorado.edu

Kristine Larson, Aerospace Engineering, CU Boulder

John Braun (UCAR/COSMIC)

Funding and support

NSF-ATM, NASA UNAVCO

Use GPS multipath for L-band environmental sensing

“ignore” direct signal

Focus on the multipath

Detrended multipath signal

Soil moisture phase shift and frequency change Vegetation amplitude

Sensing Footprint SMAP ISST, Oklahoma

~1000 m2

9 test sites: Identical GPS and hydrology infrastructure and gravimetric and vegetation sampling

SMAP ISST-C

200 m

SMAP ISST 3 standard GPS (2.5 m) 1 raised GPS (6 m)

CS616 Five at 2.5 and 7.5 cm probes outside the pen

Estimates from GPS phase shift SMAP ISST Site D

Day of Year (2010)

Vegetation water content

2.5 cm 7.5 cm

GP

S P

HI

SMAP ISST Site D GPS phase shift and CS616 soil moisture

GPS PHI

Vol.

Soi

l Moi

stur

e (x

100)

7.5 cm 2.5 cm

GPS PHI

Vol.

Soi

l Moi

stur

e (x

100)

Correlation higher with soil moisture at 2.5 cm

Estimates from GPS reflector height SMAP ISST Site A

Day of Year (2010)

Vegetation water content

2.5 cm 7.5 cm

Ref

lect

or h

eigh

t (cm

)

SMAP ISST Site A GPS reflector height and CS616 soil moisture

GPS refl height (cm)

Vol.

Soi

l Moi

stur

e (x

100)

7.5 cm 2.5 cm

GPS refl height (cm)

Vol.

Soi

l Moi

stur

e (x

100)

Correlation higher with soil moisture at 2.5 cm

Comparison to gravimetric soil moisture

ISST Site A: 2010

For 2010, GSM from calibrated theta probe

2011 efforts at ISST

Soil moisture Comparison between GPS sites, including tall antenna Comparison to in situ probes and other methods

Vegetation Identify vegetation signal in multipath data

Sensing vegetation: winter wheat site