From: Stig Syndergaard [ssy@dmi.dk] Sent: 10 February 2015 12:06 To: Burrows, Chris Cc: Culverwell, Ian Subject: Re: ROPP_PP Hi Chris, I agree with your observations for the lat, lon, azimuth interpolation in the code, and from your figures it looks like you've found a good solution. Why only temporary? No doubt that the occ_tool (and the invert_tool) has some issues. Maybe we should make a coordinated effort to get them solved for the next ROPP release. We have the ones from Kjartan, my Struct.Uncert. report, our DMI tickets (https://trac.romsaf.org/ropp/report/10) and now your investigations with GNOS - probably with some overlap. I also think we should aim at merging the occ_tool and the invert_tool (I think I've mentioned that earlier), it would make maintenance easier. Ian: Would it be possible to schedule all this for ROPP 9? -Stig On 2015-02-05 14:38, Burrows, Chris wrote: > Many thanks Stig, > > That report is very helpful indeed - it's good to know that you have seen the same features (e.g. Fig 2.5). I've come up with a temporary fix for the lat/lons (see attached), though it's not a robust solution. > > Please don't let this distract you from your other work, but any input would be gladly received! > > Thanks again > > Chris > > > > -----Original Message----- > From: Stig Syndergaard [mailto:ssy@dmi.dk] > Sent: 05 February 2015 13:18 > To: Burrows, Chris > Cc: Culverwell, Ian > Subject: Re: ROPP_PP > > Hi Chris, Ian, > > I'll have a look at this over the next couple of days (into next week); today I am just swamped in other work. I remember from the SU project some years ago that the lat, lon vector was a bit odd. And also a kink at 25 km in std.dev. I've attached the report that I did back then. At the end (section 3) there is a summary of the issues that I found. It's been on my mind to fix these things in ROPP for a while, but I never seem to get around to do it (always something more urgent). > > Best, > -Stig > > On 2015-02-05 13:19, Burrows, Chris wrote: >> Hi Stig, Ian, >> >> Just a quick update; >> >> It seems that the IPs are calculated for GO, and then, for the WO processing, the IPs below 25km are overwritten with uniformly spaced levels (keeping the size of the array the same). The lats, lons and azimuths *aren't* mapped onto these levels, so the final interpolation (https://trac.grassaf.org/ropp/browser/ropp_src/trunk/ropp_pp/tools/ropp_pp_occ_tool.f90 #L731 ) is mismatching lat,lon,azim with the post-WO impact parameters. Maybe we should store the pre-WO values for this interpolation step. It's not a huge deal, but would be important for TPD in assimilation, and 2D operators. >> >> As for the jump in standard deviations, I wonder if it's related to the fact that the WO processing outputs IPs on a fine grid (~5m in the case I was looking at). This is then interpolated onto a coarse grid, so I fear that a lot of information is being lost (this is probably consistent with large noise but small correlations). >> >> I'll keep looking into this, but I'm sure I'm not qualified to mess around with the WO settings - scary stuff... >> >> Thanks >> >> Chris >> >> >> >> -----Original Message----- >> From: Burrows, Chris >> Sent: 04 February 2015 18:28 >> To: Stig Syndergaard >> Cc: Culverwell, Ian >> Subject: ROPP_PP >> >> Hi Stig, >> >> I was looking at some sample data from the Chinese GNOS instrument with Ian today - they are using ROPP for the preprocessing. It looks pretty good but there is a sharp jump in the BA O-B standard deviations at 25km (see attached O-B stats and vertical correlations). This presumably is related to the WO/GO transition (Kjartan made reference to something similar here: https://trac.grassaf.org/ropp/ticket/293). >> >> We did a bit of further digging and what we found may or may not be related, but it is certainly confusing.... >> >> In the output file, the impact parameters are spaced equally, but there are sudden jumps in the tangent point lat-lons corresponding to IH=25km. The values do correspond to a sensible track; the transition is just due to a change in the data sampling. The azimuth also shows a suspicious jump. These are plotted in the attached 'coords.png' file (note that the jagged steps in the azimuth are due to BUFR precision; they are not present in the full-resolution files, though the 25km feature is still there). >> >> The bottom right plot is the 'angular distance', sqrt((delta lat)*2)+(delta lon)^2)) as a function of impact height (i.e. a vertical cross section of the TP trajectory) - this looks very suspicious! >> >> Similar plots are produced with GRAS data using ROPP, so we suspect there may be a bug. Do you have any thoughts about this? Perhaps the lat/lons are being overwritten incorrectly for the WO part of the processing (still sampled against time rather than a fixed IP grid?). >> >> Thanks in advance for any comments, (please copy Ian into a reply >> too!) >> >> Chris >> >> >> --- >> Chris Burrows Satellite Applications Scientist >> Met Office FitzRoy Road Exeter EX1 3PB United Kingdom >> Tel: +44 (0)1392 88 6449 >> E-mail: chris.burrows@metoffice.gov.uk http://www.metoffice.gov.uk >> >> > -- _________________________________________ Stig Syndergaard, PhD Danish Meteorological Institute Lyngbyvej 100 DK-2100 Copenhagen Phone: +45 39 157 408 E-mail: ssy@dmi.dk _________________________________________