NOAA KLM User's Guide
The Information Processing Division (IPD) of the Office of Satellite Data Processing and Distribution (OSDPD) of NESDIS supports the instrument data processing for all the operational polar orbiting satellites.. To provide accurate satellite navigation data, the IPD receives daily a set of Inertial Osculating Cartesian orbit parameters for each polar satellite from the Air Force or Navy. This orbit vector is used to generate a predicted user ephemeris file (UEF) of orbit vectors spaced one minute apart that cover a 10 day time span. This file is created using a COWELL numerical integrator (using Stormer-Cowell formulas) which maintains the one kilometer accuracy of the initial orbit vector. The UEF is the foundation for all the navigation data produced in IPD. It is utilized to create the TBUS bulletins, the equator crossing information files, the Search and Rescue (SAR) orbit ephemeris files, and Level 1b instrument data files.
The Earth location data provided in the Level 1b process is produced by the Advanced Earth Location Data System (AELDS). This system was initially implemented on September 8, 1992 in the AVHRR Level 1b process and on September 7, 1994 in the TOVS Level 1b process. It is an on-line Earth location process utilizing the scan line timecodes to produce Earth location. With the introduction of AELDS the accuracy of the Earth location data in the Level 1b file was improved by 50%.
The Earth location algorithm used to produce the latitude and longitude parameters within the AELDS process are available in Appendix I. The AELDS process provides more than just latitude and longitude information. Given the satellite position and velocity vector and the Greenwich Hour Angle (GHA), AELDS will provide the satellite height and northbound/southbound flags. Also, given the scan time, stepping time, stepping angle, and number of positions desired; AELDS can also provide the following for each scan point of a specific instrument:
In order to insure that the Earth location and navigation information provided by IPD lies within acceptable accuracy limits, quality control (QC) operations are performed during and after generation of the data. At present, three types of checks are used:
Utilization of the above image QC techniques has provided greater insight into the magnitude of Earth location errors as well as the source of some of the errors. To increase the data accuracy, IPD has enhanced the on-line Earth location process (AELDS) to include fixed attitude corrections and TIP clock corrections.
Fixed attitude corrections include corrections for errors such as instrument mounting errors and constant observed errors. An algorithm has been integrated into the Earth location process that accounts for these errors. At any time during the process, these attitude corrections may be turned on or off.
TIP clock error corrections were added to the AELDS Earth location process. The Satellite Operations Control Center (SOCC) maintains the on-board clocks for the NOAA POES satellites. They monitor the accuracy of the clocks and make adjustments whenever needed. The SOCC clock adjustments are made for two reasons:
IPD has set up a clock drift file that contains all SOCC corrections. This file is utilized to correct the Earth location data using the instrument scan times. It is made available to the user community in the following home page (URL: http://psbsgi1.nesdis.noaa.gov:8080/PSB/NAVIGATION/navpage.html).
The TBUS bulletin is a major source of orbital data for direct readout users. Although, the UEF is used in creating all four parts of the TBUS bulletin, IPD's focus is on Part IV of the bulletin. More information on the TBUS bulletin can be obtained from Section 5.1 and Appendix A. IPD, in conjunction with SOCC, has outlined steps to make Part IV more user friendly and to increase the accuracy of the data (the Brouwer Mean elements). Action has been taken in the following areas:
The IPD navigation area has established a home page on the Internet under the "Navigation/Earth Location" (URL: http://psbsgi1.nesdis.noaa.gov:8080/IPD/IPD.html). Note that the final character in "psbsgil" is the number "one". This page has links to the following existing pages:
The following entries are a part of the navigation page:
|N||REVNUM||EQ.XING.TIME (MJD)||Year||Month||Day||Hour||Min||Second||EQ.XING LONGITUDE|
|Spacecraft ID# (NOAA-14)||Effective Time||Clock Error Millisec I5||Drift Rate Millisec/Day F7.3||Comments(Optional)|
|23455||1995/12/31||23:59:59.000||-200||+5.000||-1.0 Leap Second Adjustment|
The IPD updates or enhancements to the navigation and Earth location process are on going. For example, an Earth location error database is planned for Level 1b data users. This database will contain Earth location error information based on actual error measurements taken from AVHRR imagery. The format or contents of this file has not been determined at this time. Every attempt will be made to keep the current systems compatible with both the prior satellite series and the future satellite series. As new areas are addressed, the user will see improvements in the navigation product. Comments, suggestions, or inquiries regarding the Navigation page may be sent to this email address: firstname.lastname@example.org.
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