| Paper: | WE-P3.6 |
| Session: | Cryosphere Applications of Radiometry II |
| Time: | Wednesday, March 28, 17:20 - 17:40 |
| Presentation: |
Oral
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| Topic: |
Snow, ice and oceans: |
| Title: |
SLAPEX FREEZE/THAW—A FROZEN SOIL CAMPAIGN |
| Authors: |
Edward Kim; NASA Goddard Space Flight Center | | |
| | Tracy Rowlandson; University of Guelph | | |
| | Aaron Berg; University of Guelph | | |
| | Alexandre Roy; University of Sherbrooke | | |
| | Renato Pardo; University of Guelph | | |
| | Jarrett Powers; Agriculture and Agri-Food Canada | | |
| | Kristen Lewis; NASA HQ | | |
| | Paul Houser; George Mason University | | |
| | Kyle McDonald; City College of New York | | |
| | Peter Toose; Environment and Climate Change Canada | | |
| | Albert Wu; NASA and ATA Aerospace | | |
| | Eugenia De Marco; NASA and ATA Aerospace | | |
| | Chris Derksen; Environment and Climate Change Canada | | |
| | Jared Entin; NASA HQ | | |
| Abstract: |
Permanently-frozen and seasonally-frozen soils occur over one third of the Earth’s land surface. Changes in the freeze/thaw state of the land surface are an important indicator of major changes in the thermal and hydraulic properties of the land surface as well as acting as a “switch” for many ecological processes. The surface freeze/thaw soil state is observable by passive and active microwave sensors, and NASA’s Soil Moisture Active Passive (SMAP) mission includes a soil freeze/thaw data product that now derives from the SMAP L-band radiometer after the demise of the SMAP radar.
However, relatively few airborne sensing campaigns have focused on soil freeze/thaw, so our understanding of subpixel effects and other factors that can impact freeze/thaw retrieval algorithm accuracy is limited compared with traditional summertime always-thawed soil moisture sensing. Our process-level understanding of L-band soil freeze/thaw signatures is likewise limited—in this case, by the uncertainties associated by what in-situ sensors actually report vs. sensing depths, and by the difficulties of obtaining alternative ground truth for frozen soils.
SLAPex Freeze/Thaw was an airborne sensing campaign that focused on the passive and active L-band signatures of frozen soils and soils undergoing freeze/thaw transitions. It took place over essentially bare soil agricultural fields near Winnipeg, Manitoba, Canada during the first half of November, 2015. The joint US-Canada effort included three L-band sensors: NASA’s Scanning L-band Active Passive (SLAP)--an airborne simulator for SMAP, plus two ground-based L-band radiometers—one from environment Canada and one from the University of Sherbrooke. Ground truth was collected by field teams and supplemented by automated in situ sensors.
Thirteen science flights were flown over the study area southwest of Winnipeg, coincident with the area used by the SMAPVEX12 soil moisture campaign. Five lines were flown each flight to correspond with ground truth sample locations and each day two flights were conducted in frozen (AM) and thawed (PM) conditions. Two additional "mow-the-lawn" (MTL) flights were flown to obtain full coverage of a 36x36 km SMAP pixel, the first under thawed (morning) and the second under frozen (afternoon) conditions.
This paper will describe the SLAP radiometer (and radar) calibration and performance, present airborne SLAP brightness temperature (TB) data at 250-400m resolution and comparisons with TB observations from the two ground-based radiometers. In addition to the TB comparisons, we will discuss the freeze/thaw retrievals one obtains at the different scales using the SMAP F/T algorithm, and the corresponding ground truth. Coincident radar data from SLAP will also be shown and compared with the passive data—as future low-frequency missions might benefit from such coincident passive/active observations.
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