[G01-4] Combination and co-location of space geodetic techniques

[G01-4-03] Double-Differences Over Time for Space Geodesy Techniques with GNSS Satellites and Lunar Laser Reflectors

^○Drazen Svehla, Markus Rothacher (ETH Zurich, Switzerland)

We have already demonstrated that the main advantage of common-view double-differencing of SLR measurements to GNSS is in the reduction of systematic effects, leading to differential SLR with sub-mm or mm-accuracy. Here we extend the common-view SLR approach and make double-differences over time by considering the different observation times for all SLR measurements between all SLR stations. SLR range biases and small biases between SLR sessions are removed. The scale of the reference frame is preserved after double-differencing, potentially providing access to the utmost accuracy of SLR in the global GNSS solutions. This SLR approach allows accurate estimation of local ties between SLR and GNSS, since relative coordinates between stations can be estimated independently by GNSS and SLR, thus requiring only one local tie to be estimated between ILRS and IGS ground networks. We have already demonstrated that the double-difference SLR approach with GNSS orbits from IGS offers a bias-free estimation of relative coordinates between ILRS stations with mm-accuracy separated by up to some 5000 km.

The same approach could also be applied between Lunar laser ranging (LLR) and SLR to GNSS satellites. We form double-difference LLR between two Lunar retroreflectors and two LLR stations to show the noise of the LLR of about 5-7 mm standard deviation. We managed to process LLR as one-way measurements in a geocentric frame similar to the processing of SLR to GNSS satellites and make use of the latest Lunar DE430 ephemerides and libration models. We present the estimation of the Lunar orbit and EOPs (including UT1 or UT0). This offers an interesting application of SLR and LLR in the global GNSS solutions, giving, in addition to scale, a potential access to UT1 or UT0 in the global GNSS solutions.

In the last part, we discuss a possible use of double-differences over time for the estimation of GNSS biases and resolution of integer ambiguities, as well as a possible extension to VLBI.