Technology > Calibration > NISAR Calibration
NISAR Mission
The NISAR mission is a satellite SAR jointly developed by NASA and ISRO, India's space agency. The NASA-ISRO SAR (NISAR) mission will measure our planet's changing ecosystems, dynamic surfaces, and ice masses. This will provide scientists with valuable information about biomass, natural hazards, soil moisture, and sea-level rise. See here for additional information.
NISAR Calibration
Post-launch cal/val activities will involve imaging well established ground targets. NISAR cal/val will use Corner Reflectors (CR) as these targets are commonly used for SAR systems and seventeen (17) CRs have been deployed in Oklahoma for NISAR calibration.
Oklahoma NISAR Calibration Array
The NISAR Oklahoma Calibration Array is in North (Enid), Western (Clinton), and Southern (Lawton) Oklahoma and consists of seventeen (17) 2.8-m triangular trihedral corner reflectors.
More details can be found in the kmz file below along with their precise locations.
Construction
Each NISAR CR measures 2.8 meters (9.2 ft) and is a triangular-trihedral reflector constructed with 0.125" Aluminum Alloy 5052 H32 perforated sheets with staggered round holes of size 0.188". They are retained to the ground with 1/16" guy-wires pulled down to the ground with turnbuckles attached to duckbill anchors buried 18" into the ground. The front and rear wooden platforms rest on 2" high cinder blocks attached with wedge anchors and held down by 14" metal stakes.
Deployment
Trial deployment of two NISAR CRs occurred in June, 2021 near Arapaho, Oklahoma. The images below are from left to right, N01K and N03K.
East facing CR N01K in the morning
West facing CR N03K in the evening
Coordinates
The coordinates listed are in an IGS20 Reference Frame and are expressed as WGS-84 geodetic latitude and height above the reference ellipsoid such that:
- a = 6,378,137 meters
- f = 1/298.257222
In April, 2024, a re-survey of all 17 Oklahoma corner reflectors was completed with a minimum of 8 hours of GNSS data per site. The expected RSS horizontal error from the GNSS, heading, range, and angle errors is 1.5 cm 1-sigma and the expected RSS vertical error is 1.0 cm 1-sigma. The GNSS measurements included GPS and Galileo and were processed in a Center Mass (CM) frame. Those coordinates were then converted to the Earth's Center of Figure (CF) frame to account for the Earth's geocenter motion.
Additionally the coordinates are referenced to epoch 4-June-2021 and modeled with 1.5364 cms/year of plate motion with an azimuth direction of 254°. Specifically, the changes in East, North, and Vertical are modeled as:
- delta_east_in_meters = -0.01486 * ( gps_time_past_4-June-2011_in_secs) / 365.25 / 86400
- delta_north_in_meters = -0.00428 * ( gps_time_past_4-June-2021_in_secs) / 365.25 / 86400
- delta_vertical_in_meters = 0.0 * ( gps_time_past_4-June-2021_in_secs) / 365.25 / 86400
These rates are the average of a multi-year time series analysis of the permanent CORS sites OKSY and OKCL. The PBO site WMOK for example here also shows simliar horizontal plate motion.
Nearby velocity vectors from multi-year GPS analysis
Corner Reflector (CR) Data
KMZ file of all deployed NISAR CRs in Oklahoma.
Use the 'Get Corner Reflector Data' button to retrieve the vertices of the the NISAR corner reflectors (latitude, longitude, orientation, etc) for a particular date. Data goes back to June 4, 2021. The re-surveyed positions from April, 2024 are retroactive to their installation date. After 22-May-2023, the locations of the CRs can be considered unchanged, and the complete array can be considered to be deployed after 30-Oct-2023.
Output is a comma-separated value (CSV) file. Select type tide-free for conventional tide-free crust (ITRF), select type instantaneous-crust for instantanous observed crust, and select type mean-crust for permanent tide. See for example, terrestial reference systems, particulary Figure 1.1 for additional information. The entered date applies the average plate motion of nearby GNSS sites OKSY and OKCL. The date also applies the solid tide, pole tide, and ocean tide with the FES2014b Ocean Tide Model and center of mass due to both solid Earth and ocean. The reference system instantaneous-crust is a function of latitude, longitude, and the entered time. The reference system mean-crust is a function of latitude only. See for example, permanent tide deformation.
Coordinate Type:
Get Corner Reflector Data
Use the 'Get Tide Data' button to retrieve 48 hours of the tide perturbations centered at the entered date.
Get Tide Data
Contact:
Ronald Muellerschoen
Jet Propulsion Laboratory
Mail Stop 300-243
4800 Oak Grove Drive
Pasadena, California, 91109
Tel: (818) 354-0717
Email: rjm@jpl.nasa.gov