Jitter File Product Resources
This document defines the current format of the jitter file products of the Engineering Data Processing System (EDPS). These products are similar to the Observation Logs (Obslogs) produced by the Observation Monitoring System (OMS) that no longer exists. The OMS was replaced because it was too costly to maintain and it was hosted on a platform that is no longer supported at the ST ScI. The EDPS is a less ambitious system that does not attempt to monitor instrument problems. The EDPS jitter files are limited to the engineering data that describes the performance of the Pointing Control System (PCS) including the Fine Guidance Sensors that are used to control the vehicle pointing. The jitter files report on PCS engineering data during the duration of the observation. The old name for these jitter files, observation logs (Obslogs), is now inappropriate, because of the absence of instrument monitoring. However the FITS header and extension formats of the jitter files are not radically different from the original Obslogs. FITS-based tools that access only the PCS related data should be able to handle both the old Obslogs and the new jitter files. The jitter files retain the same file naming conventions as the old obslogs.
One way to distinguish the new jitter files from the old obslogs files is to check the existence of the OPUS_VER keyword (system version id) that replaced the OMS_VER keyword. The EDPS software is part of the larger OPUS system that also supports the Science Data Processing System (SDPS) and the On-the-Fly Reprocessing (OTFR) system. Most of the format changes involve deletions of keywords. Six keywords have been added. There are some improvements in the new files. The accuracy of HST orbit-related statistics has been improved by ignoring the values in the telemetry that must be interpolated. Instead, an orbit model is used to recalculate the orbit position and velocity at the exact time needed. The new jitter files have been generated since mid-February, 2003, but there is no specific date since the OMS ran in parallel with EDPS for about a week.
The old format is well documented by the Observatory Support Web page maintained by the Telescopes Branch of the Instrument Division. This document is supplemental to the archived Observation Log (jitter file) Documentation.
Changes in image file
There are six new keywords for the jitter image file that has the file extension .jif or .jwf. Keywords that are in the primary header are assigned the extension (Ext) value 0. Keywords in other extensions have the extension value >0 since there can be more than one extension for associated products.
|ASN_PTYP||0||Association Product Type|
|GSD_FGS||0||1, 2 or 3: FGS ID of dominant FGS|
|GSR_FGS||0||1,2 or 3: FGS ID of subdominant (roll) FGS|
|GS_PRIM||0||DOMINANT or ROLL: GS that was acquired first|
|OPUS_VER||0||Build version: replaces OMS_VER|
|WCSAXES||>0||2: Number of axes for WCS parameters|
There are 43 OMS Obslog keywords that were dropped for the new jitter image file.
|OMS_VER||0||Replaced by OPUS_VER. OMS is gone.|
|EARTHMOD||0||No stray light modeling in EDPS|
|GALACTIC||0||Never implemented in OMS|
|MOONMOD||0||No stray light modeling in EDPS|
|ZODMOD||0||No stray light modeling in EDPS|
|OPERATE||0||No SI data in EDPS|
|T_ACQ2FL||0||Related keyword ACQ2FAIL is gone|
|ACQ2FAIL||>0||No SI specific data in EDPS|
|T_CLMPER||0||Related keyword CLAMPERR is gone|
|CALMPERR||>0||No SI specific data in EDPS|
|T_DCFUNC||0||Related keyword DCFUNCHG is gone|
|DCFUNCHG||>0||No SI specific data in EDPS|
|T_FGSFAL||0||Related keyword FGS_FAIL is gone|
|FGS_FAIL||>0||Astrometry specific value not supported|
|T_FOSOPN||0||Related keyword FOS_OPEN is gone|
|FOS_OPEN||>0||SI not supported|
|T_FW_ERR||0||Related keyword FW_ERROR is gone|
|FW_ERROR||>0||No SI specific data in EDPS|
|T_HVTOFF||0||Related keyword HVOLTOFF is gone|
|HVOLTOFF||>0||No SI specific data in EDPS|
|T_NO_EPH||0||Related keyword NO_EPHEM is gone|
|NO_EPHEM||>0||EDPS now gets ephemeris from database|
|T_NO_SAM||0||Related keyword NO_SAM is gone|
|NO_SAM||>0||EDPS does not monitor slews|
|T_NOSLEW||0||Related keyword NO_SLEW is gone|
|NO_SLEW||>0||EDPS does not monitor slews|
|T_SISAFE||0||Related keyword SI_SAFED is gone|
|SI_SAFED||>0||No SI specific data in EDPS|
|T_SISPND||0||Related keyword SISUSPND is gone|
|SISUSPND||>0||No SI specific data in EDPS|
|T_TAPDRP||0||Related keyword TAPEDROP is gone|
|TAPEDROP||>0||No tape recorders in HST now|
Changes in table file
The jitter table file that has the file extension .jit or .jwt has very few changes. There are still 28 columns of data in the table. Two of the columns have been replaced. Column 23 has changed from EarhMag, that was an estimate of stray light from the Earth based on a model that is no longer support by EDPS, to BrightLimb, which is a short integer value, where 1 indicated that the limb position closest to the target is bright, and 0 indicates it is dark. Column 24 has changed from SI_Specific, that is not supported by EDPS, to FGS_flags, that provides status data for all three FGS. In addition the comment for the DayNight flag has been corrected. The day value is 1 and the night value is 0. These changes affected the values of the keywords: TTYPE23, TUNIT23, TFORM23, TUNIT24, TTYPE24, and TUNIT24. The value of keyword NAXIS1 changed from 116 to 114 because the size of column 23 change from a four-byte floating value to a two-byte short integer value. The keyword ASN_PTYP was added to the association keywords. It has the same value as that keyword in the image file header.
Changes in association file structure
In the old obslogs, the jitter files for associated exposures were always collected into files with the same filename extension, .jit, .jwt, .jif, or .jwf, as the member exposures. The file name has the association rootname that is found in keyword ASN_ID. Each member exposure provides a FITS extension for a table or image, having the keyword ASN_MTYPE that describes the type of member. The primary header of the association image file has the following keywords updated to reflect statistics for the set of FITS extensions: TSTRTIME, TENDTIME, MGSSPRMS, TNLOSSES, TLOCKLOS, TNREENT, TRECENTR, TV2_RMS, MV2_P2P, TV3_RMS, MV3_P2P, TRA_AVG, TROLLAVG, T_GDACT, T_ACTGSP, T_GSFAIL, T_SGSTAR, T_TLMPRB, T_NOTLM, T_NTMGAP, T_GSGAP, T_SLEWING, and T_TFDDWN. For STIS associations, the wavecal members are separated from the science members by different file extensions: .jwt and .jwf. The structure for STIS associations has not changed. But for NICMOS and ACS, the file rootnames now match the rootnames of the association products. Only the members that are used to generate the association product are collected into FITS extension for that product. The old obslogs used only the association rootname. The new jitter-file associations may have multiple rootnames, ending in 0, 1, 2, etc. The statistical keywords in the primary header listed above are calculated for the subset of members collected for the specific association product. The ACS associations reserve the rootname of the ASN_ID for dithered data combined from multiple positions. At each position, there is an association product having the last character of its rootname being a sequence starting from 1. If there is no dithered product for ACS, the associated exposures at the single position have a product with a rootname ending in 1.
Jitter Image File Header Samples
Here is a sample of a primary header of a jitter image file.
Here is the sample image extension for the jitter image file.
Here is the list of optional keywords.
The first two keywords below occur in the primary header of the jitter image file for STIS target acquisition exposures. The optional keywords in the image extension are used for problem flags. These keywords were not present in the sample headers.
Jitter Table File Headers
Here is a sample of a primary header of a jitter table file.
Here is the sample bintable extension for the jitter table file.