fixpasstime - modify online catalog and system clock based on HRPT telemetry

fixpasstime - Modify online catalog and system clock based on HRPT telemetry

SYNOPSIS

fixpasstime  [ parameter=value ... ]

Parameters are: pass_number, fix_catalog, check_sat, fix_duration, fix_clock, max_time_adj, conseq_good.

DESCRIPTION

For a specified HRPT pass on the pass disk, fixpasstime can update the pass time in the corresponding online catalog entry to match the time embedded in the telemetry. In addition, fixpasstime can change the satellite name in the online catalog record so it matches the HRPT telemetry. fixpasstime can also change the duration in the online catalog so it is equal to the AVHRR line time multiplied by the number of AVHRR lines.

If the user's effective userid is the superuser's id, then fixpasstime can modify the system clock so it approximates the satellite time embedded in the telemetry for a given HRPT pass. fixpasstime does this by comparing the satellite time to the time appended to the end of each HRPT record by the framing process and computing a statistical average. This average correction is applied only if it does not exceed a user specified abolute limit, and only if the average's RMS error is less than .05 seconds.

PARAMETERS

pass_number: This specifies which HRPT pass to read and which entry in the online catalog to potentially modify. The default range is 1 to the maximum number of passes online. There is no default.

fix_catalog: Indicates that pass time (and possibly satellite) fields in the online catalog are to be changed to match the actual data for the selected pass. The default is yes. Even if fix_catalog=no, a corrected pass time is still reported to UNIX stderr.

check_sat: Indicates that satellite field can be changed in the online catalog to match the actual data for the selected pass. The default is yes. A corrected satellite name is written to UNIX stderr only if a correction is made.

fix_duration: Indicates that duration field should be changed to be consistent with the number of records for the selected pass. The default is no.

fix_clock: Indicates that the system clock is to be modified so it approximates the satellite clock for the selected pass. The default is no. This parameter is only used if the user's effective userid is that of the superuser, and if fix_catalog=no.

max_time_adjust: Maximum absolute time adjustment in seconds. This parameter is used only if fix_clock=yes. The valid range is between 0 and 10 seconds. The default absolute maximum adjustment is 1 second.

conseq_good: The number of consequtive HRPT frames with consistent sync, times and satellite ids required in order to verify the correct pass start time, or to compute an average system clock adjustment. The valid range is 2 to 50. The default is 10 if fix_clock=yes, otherwise the default is 3.

EXAMPLES

This is an example of fixing the pass time of pass 1 in the online catalog to correspond with the pass number on the passdisk.

cabo% fixpasstime
pass_number    : int       ? [2] 1
fix_catalog    : char(  3) ? [yes]
check_sat      : char(  3) ? [yes]
fix_duration   : char(  3) ? [no]
conseq_good    : int       ? [2]
Start time for pass 1 is  93/07/16  03:40:53.59
cabo%

FILES

onlinecat

NOTES

fixpasstime is only implemented for HRPT telemetry.

Suppose fixpasstime skips N lines before finding Conseq_lines with good times. Suppose that the time corresponding to the first of these conseq_lines is T. Then the start time of the pass is set to T - N/6. This is done so xvu Image FromPass overlays a more accurate coastline.

Last Update: $Date: 1999/05/10 20:13:53 $