An alternative derivation of the GRACE Follow-On LRI1B product: current status

Abstract

<p align="justify"><span lang="en-GB">The new Laser Ranging Interferometer (LRI) on GRACE Follow-On is measuring, just like the microwave instrument (MWI), the distance variations between the two satellites, but with a significantly higher precision. The Albert Einstein Institute (AEI) in Hannover was involved in the development of the LRI and is currently concerned with instrument operation and data analysis.  In order to verify and validate the correctness of the Science Data System (SDS) derived LRI1B data product, currently available as release 04, we started to implement an own processing chain to convert data from raw level0 or level 1A to level1B, where the latter is usually employed in gravity field recovery. Besides the validation, we are interested in testing alternative processing strategies, which could improve the data quality and that might get adopted by official processing centers at some point.<br /></span><span lang="en-GB">We will provide an overview on our processing strategy, which includes five major steps 1) Deglitching of the piston phase in order to remove phase jumps that occur when the attitude control thrusters are activated. 2) Conversion of time-tags from LRI time to GPS time and forming the phase difference of master and transponder measurements.  This removes the common 10 MHz ramp in the measurements. 3) Conversion of the phase to a physical length, the non-instantaneous biased range 4) Filtering and down-sampling of the data to the LRI1B rate of 0.5 Hz.  5) Finally, the light time correction (LTC) is calculated and allows to transform the non-instantaneous biased range and its derivatives to the instantaneous or corrected biased range. We will highlight the main differences in our processing to the RL04 processing, as far as known to us.<br /></span><span lang="en-GB">In the end, we compare the RL04 and our data set at the 1B level, which shows a slightly lower noise and uses less empirical parameters.</span></p>

Comparing GRACE-FO KBR and LRI Ranging Data with Focus on Carrier Frequency Variations

“…Finally, by employing q-constants and time-dependent frequencies in Equation ( 49), inserting Equation (46) into Equation (49), and considering the relation of carrier frequencies to USO frequencies from Table 1, one obtains…”

“…We previously derived an alternative LRI1B product from level1a data, which we label as v50 in order to distinguish it from the official v04 product [49]. A comparison of both datasets is shown for January 2019 in Figure 3.…”

Comparing GRACE-FO KBR and LRI ranging data with focus on carrier frequency variations

“…which is based on the approximation shown in eq. (27). The light propagation time in the correction term received a superscript GPS to indicate that this quantity can be obtained from the orbit product, as in eq.…”

“…We previously derived an alternative LRI1B product from level1a data, which we label as v50 in order to distinguish it from the official v04 product [27]. A comparison of both datasets is shown for January 2019 in figure 3.…”