Microwave Emission Signature of Snow-Covered Lake Ice Martti Hallikainen (1), Pauli Sievinen (1), Jaakko Seppänen (1), Matti Vaaja (1), Annakaisa von Lerber (1), Erkka Rouhe (1), Juha Lemmetyinen (2) (1) Aalto University School of Electrical Engineering (2) Finnish Meteorological Institute International Geoscience and Remote Sensing Symposium 2011 IGARSS 2011

Test site and data collection Experimental data: - Brightness temperature (TB) values - TB differences between selected frequencies - TB differences between vertical and horizontal polarization Conclusions Contents IGARSS 2011

Located in the Greater Helsinki area not far from Airport Lake Bodom (larger) and Matalajärvi (smaller and shallow; freezes earlier) Data over land collected in order to compare results for snow- covered ice vs. snow- covered terrain Scale: lower left Test Site

HUTRAD Non-Scanning Radiometer HUT-2D Interferometer 6.8, 10.65, 18.7, 23.8, 36.5 and 94 GHz 1.4 GHzdual-pol 50 deg off nadir, V and H polarization Data averaged over the Antenna beam 3.2 to 5 deg0 to 5 deg range kkkkkkkkkkkkkkkkkkkkkkkkkkkk Airborne Radiometers

Flight altitude: 300 m and 150 m 5 overpasses at each altitude Accurate localization of footprint using aircraft attitude and position Averaged brightness temperatures used in this presentation Airborne Data Collection Data collection

Off Track Error: Mostly Below 20 m

2004: April : January 30, March 20, March 26, April : January 27, February 28, March 31 (am/pm), April 14 Data include dry snow conditions and snow/ice melting period Data collected with HUTRAD radiometer (6.8 to 36.5 / 94 GHz) April 14, 2011 data collected with HUTRAD and HUT-2D (1.4 GHz) Results from 2011 flights discussed in this presentation Airborne Data

Snow temperature profile Snow density profile Snow wetness profile Snow depth Ice thickness Presence of water on ice These data collected every 100 m (except April 14, 2011) Additionally, snow grain size in selected locations In Situ Data

Example of In Situ Data: Temperature

In Situ Data: Snow-Ice Structure

Brightness temperatures at 6.8, 10.65, 18.7 and 36.5 GHz (April 14: also 1.4 GHz) (18.7 GHz: occasional interference) Horizontal polarization (V-pol not shown) TB differences between 18.7 / 36.5 GHz, and 6.8 / 36.5 GHz TB differences between vertical and horizontal polarization at each frequency (except 1.4 GHz) Results from Radiometer Measurements

Lake Bodom: Some slush below snow layer =>TB36 higher than on Lake Matalajärvi Jan 27, 2011, H-Pol, Alt 300 m

Mostly dry snow / ice Occasional water => TB6 is low Feb 28, 2011, H-Pol, Alt 300 m

Dry refrozen snow on top of ice => TB36 is low March 31 AM, 2011, H-Pol, Alt 300 m

Snow top layer getting moist => TB36 higher, but TB6 ~same as AM March 31 PM, 2011, H-Pol, Alt 300 m

Practically no snow on top of wet slushy ice layer 1.4 GHz: TB higher for Lake Matalajärvi (no in situ data available) April 14, 2011, H-Pol, Alt 300 m

Brightness temperature for Lake Matalajärvi is higher than that for Lake Bodom HUT-2D Image on April 14, 2011

Jan 27, 2011, TBH:18-36 and 6-36, Alt 300 m

Feb 28, 2011, TBH: and 6-36, Alt 300 m m

Dry refrozen snow on top of ice => low TB36 values make TB18–TB36 high March 31, 2011 AM, TBH: and 6-36, Alt 300 m

Kkkk March 31, 2011 PM, TBH: and 6-36, Alt 300 m

Jan 27, 2011, V-H, Alt 300 m

Kkkk Kkkkk Feb 28, 2011, V-H, Alt 300 m

Kkkk March 31 AM, 2011, V-H, Alt 300 m

March 31 PM, 2011, V-H, Alt 300 m

April 14, 2011, V-H, Alt 300 m

An extensive range of frequencies was used for lake ice observations 36.5 GHz provides information on dry snow, whereas low frequency penetration provides information on water at snow/ice interface Observed brightness temperature variation is substantial within Lake Bodom due to occasional presence of water on top of ice Brightness temperature for adjacent Lake Matalajärvi is different from that for Lake Bodom, obviously due to being shallow Conclusions IGARSS 2011