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 may involve imaging well established ground targets. NISAR cal/val will partially use a Corner Reflector (CR) array as these targets are commonly used for SAR systems. 17 corner reflectors will be located in NISAR's swath over the Oklahoma and will be deployed for NISAR calibration.
Oklahoma NISAR Calibration Array
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 here are in IGS14 Reference Frame. See a chronology of reference frames for additional information. The coordinates are expressed as WGS-84 geodetic latitude and height above the reference ellipsoid such that:
- a = 6,378,137 meters
- f = 1/298.257222
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 GPS multi-year GPS analysis
Corner Reflector (CR) Data
KMZ file of all deployed NISAR CRs in Oklahoma. Orange triangles represent deployed CRs while Green triangles represent CRs to be deployed Oct 19-Oct 31, 2023
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. 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 300-238
4800 Oak Grove Drive
Pasadena, California, 91109-8099
Tel: (818) 354-0717
Email: rjm@jpl.nasa.gov