Know Your Earth 3.0: AirMOSS
About Alexandra Chau
Alexandra H. Chau joined NASA's Jet Propulsion Laboratory Radar Science and Engineering Section in Pasadena, Calif. as a radar systems engineer; her job entails radar performance model development, system trade studies, system-level data analyses, science data analyses, algorithm development and performance characterization. One of her first projects was analyzing test data and verifying performance requirements of the landing radar for the Mars Curiosity Rover. In addition, she has worked on several spaceborne and airborne missions for Earth observation and Mars exploration, including missions like Quick Scatterometer (QuikScat), Soil Moisture Active-Passive (SMAP), Interior Exploration using Seismic Investigations, Geodesy and Heat Transport (InSight) and Airborne Microwave Observatory of Subcanopy and Subsurface (AirMOSS).
A keystone of the AirMOSS mission is the airborne P-band synthetic aperture radar (SAR) system, which provides calibrated polarimetric backscatter measurements that are used to derive root-zone soil moisture. In the planning stages of AirMOSS, Chau contributed to modeling the SAR system performance, which guided the radar system design and defined its key operational parameters. Later, as the SAR system was being built and tested, Chau worked as part of the team that determined the testing suite and analyzed the resulting data to ensure that the system was performing as expected.
As a systems engineer, part of Chau's role is to serve as the critical bridge between the engineers who design, build, and test the SAR and the scientists who translate the radar measurements into root-zone soil moisture estimates and plug them into the climate models. This involves working with the science team to understand how they use the radar data and how accurate they need to it be, while simultaneously working with the rest of the engineering team to make sure that the SAR system will meet the scientists' needs.
Chau graduated from Roswell High School in Roswell, Ga. She attended Massachusetts Institute of Technology in Cambridge, Mass. and received her Bachelors of Science, Masters Degree, and Ph.D. in mechanical engineering. Her graduate research used biomedical optics to study atherosclerosis via application of optical coherence tomography and raman spectroscopy techniques.
North American ecosystems are critical components of the global carbon cycle, exchanging large amounts of carbon dioxide and other gases with the atmosphere. Net ecosystem exchange (NEE) quantifies these carbon fluxes, but current continental-scale estimates contain high levels of uncertainty. Root-zone soil moisture and its spatial and temporal heterogeneity influence NEE and contribute as much as 60 to 80 percent to the uncertainty. The goal of the Airborne Microwave Observatory of Subcanopy and Subsurface (AirMOSS) project is to provide a new NEE estimate for North America with reduced uncertainty. AirMOSS reduces this uncertainty by providing high-resolution observations of root-zone soil moisture over regions representative of the major North American biomes, quantifying the impact of root-zone soil moisture on the estimation of regional carbon fluxes and upscaling the reduced uncertainty estimates of regional carbon fluxes to the continental scale of North America.
AirMOSS uses airborne ultra-high frequency synthetic aperture radar capable of penetrating through substantial vegetation canopies and soil down to depths of approximately 3.9 feet (1.2 meters). For AirMOSS, a modified version of NASA's Uninhabited Aerial Vehicle Synthetic Aperture Radar is flown on a Gulfstream-III aircraft. Extensive ground, tower, and aircraft in situ, on-site, measurements are used to validate root-zone soil measurements and carbon flux model estimates.
The AirMOSS root-zone soil moisture benchmark datasets, a first of their kind, will be a major breakthrough over current point-scale root-zone soil moisture measurements and will provide a critical set of input parameters to carbon flux models. AirMOSS science data products include root-zone soil moisture at 0.06 mile (100-meter) resolution, estimates of this moisture at continuous time samples through hydrologic data assimilation, estimates of NEE at 0.06 mile (one-kilometer) resolution and arbitrary time scales through ecosystem demography modeling, and upscaled North America NEE estimates at 31.0 mile (50-kilometer) resolution. In situ measurements will also be archived, including ground sensor measurements, ground sensor precipitation measurements and atmospheric tracer flux measurements. The project will conclude with a new estimate of North American NEE and a quantitative assessment of the reduced uncertainty.
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