From wlee@stout.atd.ucar.edu Tue Sep 12 13:20:43 1995 From: wlee@stout.atd.ucar.edu (Wen Chau Lee) Subject: VORTEX data message #2 Dear VORTEX data users: The longitude data on ELDORA field tapes were recorded incorrectly (most likely 0). Therefore, merging longitude, latitude and altitude information from the NCAR RAF ADS dataset is strongly recommended for all VORTEX data (field format tape). Otherwise, you will find your dual-Doppler analyses looking strange. GPS data were not recorded on ELDORA field tapes. Users have to merge GPS data from the ADS dataset to replace the INS data recorded on the tape. Prior to 6 May 1995, one of the radar frequencies interfered with the GPS receiver on the Electra preventing normal operations of GPS. Users should not attempt to merge GPS data for flights between 17 April and 2 May 1995 but instead merging the INS data to correct the recording problems in the field tape. When GPS data is available, it is preferable to merge GALT (GPS altitude) into PALT(pressure altitude). PALT is computed using standard atmosphere parameters and can be off by a few hundred meters in certain cases. Also, HGME (aircraft altitude from the radar altimeter) should be merged into HGME explicitly because HGME was not available in real time for ELDORA (see example below). The following are the documents on how to obtain VORTEX ADS data in netcdf format from stout's ftp directory, how to unpack the tar file and segments of the translator script that can be used to implement these merges. Please contact me if you have more questions. Wen-Chau Lee ************************************************** MERGE RAF netCDF AIRBORNE DATA WITH ELDORA DATA Step 1: ftp the file: stout:/global/pub/snorman/raf_cdf.tar.gz Step 2: uncompress the file using the command 'gunzip raf_cdf.tar.gz' Step 3: untar the files using the command tar -xvf raf_cdf.tar Step 4: edit your translator script to include the following environment variables; AC_NETCDF_FILES & AC_NETCDF_ALIASES (see example below). For a detailed description of the environment variables, you can refer to the website: http://www.atd.ucar.edu/rdp/solo/data_tran.html#EVL ************************************************** TRANSLATOR EXAMPLE: setenv AC_NETCDF_FILES "/net/port/vortex/raflrt/22may95.cdf " This specifies a merge of RAF netCDF airborne data with the radar platform descriptor parameters and also specifies what file is to be used. Currently this should be a "low-rate" tape. The default set of RAF netCDF field names used is: "HGME PITCH ROLL THDG VEWC VNSC VSPD LATC LONC PALT UIC VIC WIC". setenv AC_NETCDF_ALIASES "LATC < LAT LONC < LON PALT < GALT HGME < HGME \ PITCH < NOT ROLL < NOT VEWC < NOT VNSC < NOT THDG < NOT \ UIC < UI VIC < VI WIC < WP3" Allows substitution for the default fields of the raf netcdf aircraft data tape which are used to revise various platform descriptor parameters. Fields not referenced will use the default name. If you wish not to replace some of the fields then you can indicate this with the entry: ROLL < NOT and the roll will not be replaced. If you wish to substitute only one or two fields you can say "ONLY HGME < HGME LONGC < LON" ************************************************** NOTE: If a netCDF files has the extension 'fixed' (ie: 30apr95.fixed.cdf), you should use the fixed version. There was some problem with the original netCDF files, but this has been fixed. ****************************************************************************** ****************************************************************************** Obtaining ATD Data Through Anonymous FTP ======================================== [Note: NCAR ATD provides PAM, CLASS, ISS, aircraft, and radar data; ATD also may act as a conduit for other agencies' data sets. When using ATD data, or any "value added" data product created by ATD, you implicitly agree to appropriately acknowledge NCAR and the National Science Foundation in any publications or reports. Additionally, you should be sure to properly acknowledge other agencies when using their data.] NCAR Atmospheric Technology Division data can be made available upon request for acquisition via anonymous ftp (file transfer protocol). To obtain such data, follow these steps: 1) Request that the necessary data be prepared for ftp. Such a request can be made through e-mail, phonecall, or letter to the Atmospheric Technology Division's Research Data Program (ATD/RDP). You will be notified (preferably by e-mail) when your data are available for recovery. 2) Know the name of the file(s) you wish to recover. 3) ftp to the ATD machine with the following command: ftp ftp.atd.ucar.edu or ftp 128.117.78.19 Note that this machine can be reached only through internet. 4) When prompted for a login, type: anonymous or, from a DEC machine running VMS, use "anonymous" 5) When prompted for a password, enter your last name or your system login ID. You are now logged in through ftp to the ATD ftp server. You are in a special directory, and your access to the rest of the ATD filesystem is restricted. Use the ftp "help" command if you are unfamiliar with the use of ftp. Under most circumstances, the data you have requested will be in the subdirectory called pub. Try the following commands: ftp> ls ftp> cd pub ftp> ls Here, the ftp> indicates the system prompt, and is *not* something that is to be typed by you. The first command lists several subdirectories; the second command changes directory to the subdirctory pub, and the third command lists the files in pub. Identify the file you wish to recover. Let's assume it's called "myfile". You should know ahead of time if the file can be considered ASCII or binary data. ASCII is best considered as pure text, with "newline" (often a null character) line delimiters; ASCII files can be readily viewed in a text editor. If the file is binary (most ATD datasets will be binary), issue the command: ftp> binary Then, get your file: ftp> get myfile myfile.cpy This command will get the file "myfile", and copy it to the current working directory on your local system as "myfile.cpy". Note that if you had not specified the second argument ("myfile.cpy"), the file would have been copied to "myfile" in your present working directory. FTP *will* over-write any files in your local directory with the same name as the file you are trying to get. Often, the data you wish to obtain will be packaged in a UNIX "tar" file. This tar file may or may not be compressed (see your UNIX "man" pages on the commands "tar" and "compress"). If the file is a tar file, it will be indicated by a filename extension. For example, you'd have the filename "myfile.tar". If the file is compressed, an extension of ".Z" will be added to the filename. A compressed tar file would have a name such as "myfile.tar.Z". Note that both tar files and compressed files should be considered "binary" for purposes of ftp. After you obtain all your files, exit ftp: ftp> quit Please inspect your data as soon as possible after you obtain them. At a minimum, check the byte length of any received files against the length of the corresponding files as seen during your ftp session (while in ftp, do "ls -l"); file length should not vary between systems. Note that ATD's disk space is limited, and it will be necessary to remove your files from the ftp space as soon as you recover them (please send your contact at ATD a message stating that data recovery was successful!)