Synthetic aperture radar (SAR) data from the European Space Agency's (ESA) Sentinel-1A satellite were acquired for this study from the Alaska Satellite Facility and used to generate spatially detailed land-surface deformation maps (interferograms) for the Pajaro Valley during 2015 through 2018 using conventional Interferometric Synthetic Aperture Radar (InSAR) workflows.

GPS data collection: GPS measurements were taken at 24 geodetic monuments during September 27-October 2, 2015. The GPS surveys generally followed established guidelines (Zilkoski and others, 1997), except that the data were processed with single-baseline, rather than multi-baseline, software. GPS measurements were recorded at the monuments on at least 2 different days during 1-hour observation periods. Of the 24 geodetic monuments, 7 were network control stations—DUNE, COCH, DEEP, CAHU, PAIN, C101, and G70; GPS measurements were recorded at these seven stations on 3 additional days during 6.5-hour (or longer) observation periods. InSAR data collection: The data set consists of twenty-four individual interferograms and two stacked interferograms. Of the twenty-four individual interferograms, two interferograms were processed from synthetic aperture radar data acquired by the German Aerospace Center’s (DLR) TerraSAR-X satellite and twenty-two interferograms were processed from synthetic aperture radar data acquired by the European Space Agency’s (ESA) Sentinel-1A satellite. The two stacked interferograms were created by summing multiple individual interferograms. Radar data used to produce the interferograms shown in this report were obtained from the European Space Agency through their free and open data policy and the German Aerospace Center through research proposal GEO1609 for purposes of research and development.

The Central Valley, and particularly the San Joaquin Valley, has a long history of land subsidence caused by groundwater development. The extensive withdrawal of groundwater from the unconsolidated deposits of the San Joaquin Valley lowered groundwater levels and caused widespread land subsidence—reaching 9 meters by 1981. More than half of the thickness of the aquifer system is composed of fine-grained sediments, including clays, silts, and sandy or silty clays that are susceptible to compaction. In an effort to aid water managers in understanding how water moves through the aquifer system, predicting water-supply scenarios, and addressing issues related to water competition, the United States Geological Survey (USGS) developed a new hydrologic modeling tool, the Central Valley Hydrologic Model (CVHM; Faunt and others 2009). For a more detailed description of satellite-based InSAR methods, please see Sneed and others (2013; 2018). For a more detailed description of UAVSAR, please see https://uavsar.jpl.nasa.gov/education/what-is-uavsar.html. The data presented in this data release was provided by Sneed and others (2013; 2018) and will be used to facilitate updates from CVHM to CVHM2 and represent subsidence observations (measurements) using satellite and airborne Interferometric Synthetic Aperture Radar (InSAR) data during 2003–2016. In the context of this report, subsidence is defined as the lowering of the land-surface elevation as a result of aquifer-system compaction and is calculated by differencing repeated elevation measurements. InSAR methods have been used to monitor land subsidence in the Central Valley and are discussed in more detail in the following sections.

Synthetic aperture radar (SAR) data from the European Space Agency's (ESA) Sentinel-1A satellite were acquired from the Alaska Satellite Facility and used to generate spatially detailed land-surface deformation maps (interferograms) for the Pajaro Valley during 2015 through 2018 using conventional Interferometric Synthetic Aperture Radar (InSAR) workflows. Groundwater level data collected by the Pajaro Valley Water Management Agency during 1970 to 2018 was provided to USGS and used to assess changes in groundwater levels as it relates to aquifer system compaction and resultant land subsidence in the Pajaro Valley.

Extensive groundwater withdrawal from the unconsolidated deposits in the San Joaquin Valley caused widespread aquifer-system compaction and resultant land subsidence from 1926 to 1970—locally exceeding 8.5 meters. The importation of surface water beginning in the early 1950s through the Delta-Mendota Canal and in the early 1970s through the California Aqueduct resulted in decreased groundwater pumping, recovery of water levels, and a reduced rate of compaction in some areas of the San Joaquin Valley. However, drought conditions during 1976–77, 1987–92, and drought conditions and operational reductions in surface-water deliveries during 2007–10 decreased surface-water availability, causing pumping to increase, water levels to decline, and renewed compaction. The U.S. Geological Survey, in cooperation with the California Department of Water Resources, assessed more recent land subsidence near a 145-kilometer reach of the California Aqueduct in the west-central part of the San Joaquin Valley using Interferometric Synthetic Aperture Radar (InSAR) methods. Analysis presented in Sneed and others (2018) is based, in part, on subsidence contours derived from InSAR data for January 2008–January 2010, and are presented in this data release.

This dataset contains AirSWOT interferogram products collected during the 2021 Delta-X Campaign over the Atchafalaya and Terrebonne Basins of the Mississippi River Delta, Louisiana, USA from 2021-03-26 to 2021-04-18 (Spring) and 2021-08-21 to 2021-09-12 (Fall). AirSWOT uses near-nadir wide-swath Ka-band radar interferometry to measure water-surface elevation and produce continuous gridded elevation data. AirSWOT elevation data is useful for calibrating elevation and slopes along the main channels, as well as tying observations to open ocean tidal conditions. The AirSWOT Level 1B (L1B) data products represent interferogram data in the radar coordinate system, not in georeferenced map coordinates. This is an earlier stage of data processing which is used to generate the later Level 2 and Level 3 data products which will contain georeferenced water heights and water height profiles for river channels in each basin. The data are provided in binary and text file formats.