From: Henno.Boomkamp@esa.int To: igsleo@igscb.jpl.nasa.gov Message-ID: <41256AC5.0049BDD6.00@esoc.esa.de> Date: Wed, 12 Sep 2001 14:22:24 +0100 Subject: [IGSLEO-14] CHAMP orbit test period Sender: owner-igsleo Precedence: bulk ****************************************************************************** IGS LEO Mail 12 Sep 05:33:21 PDT 2001 Message Number 14 ****************************************************************************** Author: Henno Boomkamp Dear Colleagues, Events in the United States urge me to start with an apologee towards the American groups for this 'business as usual' mail. I was writing this yesterday just when the news started to come in, and attention shifted towards the news channels. At ESOC as anywhere else in Europe we feel affected by what is happening, but continuing with normal work is probably not a bad response. I removed any mention of deadlines though, because contributions from the USA groups are especially appreciated even if there may be some delays. The purpose of this mail is to take concrete steps towards exchanging CHAMP POD results between the various IGS LEO pilot project groups. Several Associate Analysis Centres of the pilot project are reaching a more or less mature level of CHAMP orbit determination, and would like to have some external orbits for verification purposes. I therefore propose that all AACs that are reasonably capable of producing CHAMP orbits prepare POD solutions for a specific period, namely for the interval 2001/140 to 2001/150 = May 20 to May 30 of 2001 (11 days) This period corresponds to some of the earliest days for which the CHAMP data became available to the IGS LEO PP groups, and as a result they appear to be quite well analysed by various centres. I expect that several AACs will already have orbit solutions for these days on file. Carey Noll has offered to set up a CHAMP orbit repository at CDDIS, which seems convenient for all of us. The precise format for implementing this repository is still under preparation, but it will be very similar to what is already in place for GPS. As a first step in the orbit exchange campaign, I would like to ask all interested AACs to respond to this mail, and indicate if and when your own orbit solutions for the above test period could be made available. Even if you are not yet satisfied with the current precision of your orbits (... this also applies to us at ESOC) it may be useful to take part in this exchange, simply for having the external references. Practical instructions for uploading and downloading will follow later. In principle the SP3 format will be used for exchanging orbits, but a particular CHAMP standard for the formatting characteristics has not yet surfaced (arc lengths, vector interval, velocity included, clock bias included, ...) My recommendation would be the following: - 24 hour files, from 00:00 to 24:00 (GPS time) - 1 minute intervals between vectors - Velocity vectors also included in the files - Satellite identifier for CHAMP is L06 A more definitive standard for CHAMP SP3 should be an outcome of this first orbit exchange campaign. For comparing orbits, I'm preparing a flexible orbit comparator program that will interpolate in SP3 input files whenever necessary, and will perform a 7-parameter transform to show reference system differences. This means that, within reason, deviations from the above format can be tolerated at least until a clear CHAMP standard is consolidated. This tool can also be made available to those AACs who do not yet have a similar comparator, but would like to do some comparisons themselves. For the longer term, ESOC plans to work towards a routine CHAMP orbit product that will typically be 24 hr delayed w.r.t. real-time, due to data availability. We hope that a reasonable number of other AACs will also start producing near real-time CHAMP orbits in the not so distant future, in which case ESOC can offer to take care of routine comparisons, or a form of combination solution. If any AACs can already confirm that they will contribute routine CHAMP orbits at some point, I would be interested to find out, but more about that later. Please note that taking part in the above CHAMP orbit exchange does not imply any commitment from your AAC to participate in routine CHAMP orbit computations at a later stage, so please participate if you can. Best regards, Henno Boomkamp IGS LEO Pilot Project AAC coordinator