on the use of observations from the aquarius/sac-d mission to study the cryosphere emmanuel dinnat...

On the use of observations from the Aquarius/SAC-D mission to study the cryosphere

Emmanuel Dinnat1,2 and Ludovic Brucker1,3

1. Cryospheric Sciences Laboratory, NASA GSFC, Greenbelt, MD, USA

2. Chapman University, Center of Excellence in Earth Systems Modeling & Observations, Orange, CA, USA

3. Universities Space Research Association, GESTAR, Columbia, MD, USA

Dinnat and Brucker, Aquarius Science Team Meeting, Seattle, WA, U.S.A.11/14/2014

Acknowledgement:

Ludovic Brucker in a storm somewhere in Antarctica …

Dinnat and Brucker, Aquarius Science Team Meeting, Seattle, WA, U.S.A.

• Analyze data spatial distribution• Assess the observations' stability• Contribute to define cal/val and intercalibration

experiments

11/14/2014

Þ Create product adapted to high latitudes

Use L-band observations to study the cryosphere.

Motivations

Aquarius Tb/NRCS availablealong track only


Presentation of the high latitude product

Brightness temperatures over Greenland and Antarctica

Radar measurements over Antarctica

Ocean freshening and ice melt

11/14/2014

Outline


Input data sets: Aquarius Level 2 swath data (PO.DAAC, version 3.0)

Spatial coverage: latitudes > 50°

Temporal resolution: 7 days

Grid cell size: 36 km × 36 km

Grid: Equal-Area Scalable Earth (EASE2.0) (Brodzik et al., 2012)

Þ constant resolution in polar regionsÞ consistent with SMAP

11/14/2014

New Aquarius weekly polar-gridded products








11/14/2014


#RFI

ASC DSC








11/14/2014


#RFI

ASC DSCLarge RFI reduction in 2014


Brightness temperature (TB)

at V & H polarizations

for radiometers 1, 2, and 3 (separately)

for ascending orbits, descending orbits, and combined

Normalized radar cross section (NRCS)

at VV, VH, & HH polarizations

for beams 1, 2, and 3 (separately)

for ascending orbits and descending orbits separately

Sea surface salinity (SSS)

for radiometers 1, 2, 3, and all combined

for ascending orbits, descending orbits, and combined

Þ Weekly mean and stdev, number of observations, and ice fraction11/14/2014



Radiometer #3 ~ 46°, V-pol

Brightness Temperature, Greenland, 2013

Jan March May

July Sept Nov


L-band TB shows no seasonal/temperature variations, but summer variations due melt and refreeze.

South Dome, Greenland, Tb time series

11/14/2014


Summit, Greenland, Tb time series


Surface reflection is an important radiative transfer process

even when the radiation has a large penetration depth

In 2012, surface layer of refrozen snow => - 5 K

Summit, Greenland, Tb time series


Lower Tb inland (dry snow zone), higher Tb near coast, with maximum extent in January because of melt

Brightness Temperature in Antarctica

Sept Nov Jan

JulyMayMarch


Areas where melt events occurred since August 1, 2000 were masked.Standard deviation < 1 K.

East AntarcticaAnnual mean and standard deviation TB (Beam 1)


Temperature below 15 m:

218.42 ± 0.07 K (Brucker et al., 2011)

Snow accumulation:

8-10 cm of snow (Urbini et al., 2008)

11/14/2014

Ideal site to study the relationship between microwave observations & ice properties

Dome C, Antarctic Plateau (3240 m)


Fast variations = surface changes

Dome C - 1.4 GHz TB time series

Beam TB V (K) 3 209.50 ± 0.26 2 206.79 ± 0.25 1 202.54 ± 0.28

Beam TB H (K) 1 189.97 ± 0.44 2 186.22 ± 0.53 3 181.39 ± 0.72

Sensitivity ~ 0.2K

11/14/2014


AMSU-B grain index derived from AMSU-B (Picard et al., 2012),

GI = 1 - TB150/TB89 with shallow penetration (few cm) channels

Satellite monitoring of the snow surface at Dome C


Aquarius radiometers• have an excellent sensitivity (0.2 K)• are thus appealing to study the ice sheets

TB variability at H polarization• is larger than at V polarization• increases as incidence angle increases• is larger than the sensors' sensitivity

L-band radiation• has a deep penetration• but is sensitive to surface snow properties

11/14/2014

Brucker et al., 2014: Effect of Snow Surface Metamorphism on Aquarius L-Band Radiometer Observations at Dome C, Antarctica. IEEE TGRS 52(11): 7408-7417, doi:10.1109/TGRS.2014.2312102.

Main conclusions for L-band radiometry of the cryosphere


AntarcticaNormalized radar cross section (NRCS, beam 3)

Asc.

Dsc.

VV HHVH


NRCS over Antarctica

Radarsat (RAMP) DEM Drainage system boundaries


No measurements currently characterize melt water flux

Can Aquarius SSS retrievals be helpful?

Aquarius observations to monitor Greenland ice sheet meltGreenland mass loss rate has increased significantly in last two decades (Sheppard et al., 2012)


Impact of sea ice on SSS retrievals


Studying freshening from ice sheet melt requires correction for sea iceÞ Sea ice emission model needed



Tb is very sensitive to sea ice …



… and sea ice concentration is uncertain.


Ove

r-es

timat

ed

sea

ice

conc

entr

ation


• 3 weekly polar-gridded products are available with Aquarius:

• * Brightness temperature• * Normalized radar cross section• * Sea surface salinity

• http://nsidc.org/data/aq3_tb.html• http://nsidc.org/data/aq3_nrcs.html• http://nsidc.org/data/aq3_sss.html

11/14/2014

• Brucker, Dinnat and Koenig (2014), “Weekly gridded Aquarius L-band radiometer/scatterometer observations and salinity retrievals over the polar regions -- Part 1 & 2”, The Cryosphere.

• Relevant for studying:• - ice sheets• - sea ice• - frozen soil• - freshening

Conclusion

http://nsidc.org/data/aq3_tb.html

http://nsidc.org/data/aq3_nrcs.html

http://nsidc.org/data/aq3_sss.html


Sheppard et al. 2012


RFI over Greenland / North polar regions -- 2013

Ascending passes Descending passes


RFI over Greenland / North polar regions -- 2014

Ascending passes Descending passes


Penetration Depth


Hoar crystal on the surface

on the use of observations from the aquarius/sac-d mission to study the cryosphere emmanuel dinnat...

Documents

descending orbits

ascending orbits

aquarius science team

aquarius level

hh polarizations

antarctica slide

usa slide

ludovic brucker