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Title: Comparison of airborne passive and active L-band System (PALS) brightness temperature measurements to SMOS observations during the SMAP validation experiment 2012 (SMAPVEX12)

item COLLIANDER, ANDREAS - Jet Propulsion Laboratory
item Jackson, Thomas
item MCNAIRN, H. - Agriculture And Agri-Food Canada
item CHAZNOFF, S. - Jet Propulsion Laboratory
item DINARDO, S. - Jet Propulsion Laboratory
item LATHAM, B. - Jet Propulsion Laboratory
item O'DWYER, I. - Jet Propulsion Laboratory
item CHUN, W. - Jet Propulsion Laboratory
item YUEH, S. - Jet Propulsion Laboratory
item NJOKU, ENI - Jet Propulsion Laboratory

Submitted to: Geoscience and Remote Sensing Letters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/19/2014
Publication Date: 4/1/2015
Publication URL:
Citation: Colliander, A., Jackson, T.J., McNairn, H., Chaznoff, S., Dinardo, S., Latham, B., O'Dwyer, I., Chun, W., Yueh, S., Njoku, E. 2015. Comparison of airborne Passive and Active L-band System (PALS) brightness temperature measurements to SMAP observations during the SMAP Validation Experiment 2012 (SMAPVEX12). Geoscience and Remote Sensing Letters. 12:801-805.

Interpretive Summary: Microwave brightness temperatures obtained by an aircraft-based sensor were compared to those measured by a satellite instrument, which demonstrated that higher spatial resolution data scale to coarser resolution. Aircraft-based measurements are invaluable for the development of spaceborne remote sensing retrieval techniques; however, it is also important that the airborne observations are related to the spaceborne measurements. This is especially true in estimating soil moisture using low frequency microwave techniques because the spatial resolution of satellite instruments is coarse, which makes it very difficult to characterize heterogeneous conditions within the footprint. The European Space Agency’s (ESA) Soil Moisture and Ocean Salinity (SMOS) satellite was available during an extended field campaign conducted to support the upcoming Soil Moisture Active Passive (SMAP) satellite. This provided a unique opportunity to evaluate spatial scaling. The correspondence of the measurements obtained in this experiment will support the use of the aircraft data set in the development of soil moisture retrieval algorithms the upcoming Soil Moisture Active Passive satellite.

Technical Abstract: The purpose of SMAP (Soil Moisture Active Passive) Validation Experiment 2012 (SMAPVEX12) campaign was to collect data for the pre-launch development and validation of SMAP soil moisture algorithms. SMAP is a National Aeronautics and Space Administration’s (NASA) satellite mission designed for the measurement of soil moisture and freeze/thaw state and is scheduled for launch in November 2014. SMAPVEX12 was conducted in the vicinity of Winnipeg, Canada, in the summer of 2012. On 17 days between June 6 and July 17, brightness temperature and backscatter measurements were collected with the PALS (Passive Active L-band System) concurrent with in situ soil moisture measurements. The conditions during the campaign covered almost the full range of soil moisture (from less than 0.1 m3/m3 to more than 0.4 m3/m3) and vegetation (from bare soils to crops with vegetation water content more than 5 kg/m2 to forested areas) conditions for the region. The general responses of Passive Active L-band System (PALS) corresponded to the in situ observations as expected. In this study it is shown that same day spaceborne observations made by the European Space Agency’s (ESA) Soil Moisture and Ocean Salinity (SMOS) satellite agreed closely with the PALS brightness temperature acquisitions. The difference between the measurements was less than 5 K and 6 K for vertical had horizontal polarizations, respectively, over the relatively homogeneous agricultural areas. These values are less than the SMOS sub-pixel variability determined from the PALS measurement. This result demonstrated that the measurements obtained in the experiment are scalable to spaceborne brightness temperature observations, are representative of the expected SMAP observations, and will be of value in the development of soil moisture algorithms for spaceborne missions.