GRACE-FO: Reflector Information
View of the GRACE-FO LRR
Required orientation of the LRR with respect to the GRACE-FO S/C velocity
vector
Images courtesy of GFZ Helmholtz Center, Potsdam
RetroReflector Array (RRA) Characteristics:
The LRR consists of four optical cube corner reflectors which are optimised in their far field diffraction pattern to correct for the effect of light velocity aberration due to the relative motion between satellite and ground station to a high degree. The ranging signal from the transmitting ground station is reflected back to its origin independently from its angle of incidence as long as the cut-off entrance angle is not exceeded.
The LRR design is pyramid shaped with the outer surfaces inclined by 45 degrees with respect to the mounting plane. This ensures that for elevations exceeding 20 degrees above the SLR ground station the angle of light incidence to the individual prisms is below the cut-off angle and laser ranging is enabled.
The LRA is identical in design to the arrays flown on CHAMP, GRACE, Swarm, TerraSAR-X and others. Detailed information can be found at https://ilrs.cddis.eosdis.nasa.gov/docs/rra_champ.pdf and in the GRACE Follow-On Laser Retro Reflector User Manual.
GRACE Follow-On Laser Retro Reflector User Manual (11-Oct-2015)
Contact information:
Name: Sven Bauer
Organization and position: GFZ, SLR station manager
Address: Telegrafenberg, 14473 Potsdam, Germany
Phone number: +49-331-288-1733
E-mail address: sven.bauer@gfz-potsdam.de
LLR coordinate system:
The following coordinate system is chosen for the LRR with its origin in the invariant point of the array (intersection of all optical prism axes):- X-axis: along the diagonal of the mounting surface, i.e. parallel to the engraved double arrow in the structure; positive along to the S/C velocity vector.
- Z-axis: along the rotational symmetry axis of the array (through the geometric center of the mounting surface). According to the mounting of the LRR at the nadir side of the GRACEFO S/C this means that Z is positive towards nadir.
- Y-axis: completing the right-hand orthogonal system. Azimuth angle positive along track, nadir angle positive towards nadir.
Position (XYZ) of the center of the front face of each corner cube, and the orientation (two angles or normal vector) and the clocking (horizontal rotation) angle of each corner cube:
X, Y, Z, in mm; Azimuth, Nadir angle in degrees; prism numbering in clockwise direction
Prism 1: +25, +25, +33.5; +45, +45
Prism 2: +25, -25, +33.5, -45, +45
Prism 3: -25, -25, +33.5, -135, +45
Prism 4: -25, +25, +33.5, +135, +45
Coordinates of front surface centers given in LRA coordinate system as defined above.
Related information:
- ILRS GRACE-A, -B mission pages
- NASA JPL's GRACE website
- GFZ - Potsdam's GRACE web page
