NOAA KLM User's Guide
The NOAA KLM POES satellites begin a new era of improved environmental monitoring in support of NOAA missions. The instrument payload has significant improvements and additions/deletions. The instrument changes have effected the spacecraft subsystems and data formats.
The NOAA KLM satellites include improvements to instruments that are evolutionary and significant. The initial concept was to add more passive microwave instruments and channels in place of the four channel Microwave Sounding Unit (MSU) and the three channel Stratospheric Sounding Unit (SSU). During the satellite system design process, it became evident that the increased size, fields of view, and power requirements for the new instruments would have significant impacts on the spacecraft power, data handling, and attitude control systems. The NOAA KLM spacecraft are significantly heavier than previous spacecraft (2231.7 kg versus 1712.3) and require a more powerful Apogee Kick Motor (AKM) solid rocket booster and expendable launch vehicle, TITAN-II, to obtain orbit. Combined with command system security and frequency changes, NOAA KLM satellites look very much like previous satellites to the casual observer, but have significant changes to essentially every subsystem. To meet the increased power requirements, two additional solar panels have been added and the solar array has about 45% more output. The batteries, propulsion tank capacity, the size of the reaction wheels and magnetic coils used for momentum unloading and attitude control have also increased in capacity. The spacecraft structure has been stiffened primarily to support the heavier AMSU instruments and improve launch vehicle load margins. Several antennas have been relocated and/or built with new materials and processes to improve performance. Flight computer memory has been doubled and the flight software modified to meet new requirements.
The Advanced Microwave Sounding Units (AMSU-A1, AMSU-A2, AMSU-B) are state-of-the- art passive microwave sounders that will significantly enhance NOAA's atmospheric sounding and non-sounding products suite. AMSU is expected to improve global sounding (especially in the presence of clouds), water vapor profiles and information on precipitation and ice. The AMSU instruments have better spatial resolution and upper atmospheric sounding capabilities than the previous MSU instrument flown on the TIROS-N series.
The Advanced Very High Resolution Radiometer (AVHRR/3) provides spectral and gain changes to the visible channels that will allow improved low energy/light detection and adds a sixth channel, called 3A, at 1.6 μm for improved snow and ice discrimination. Scan mechanism lifetime and jitter performance have been improved with changes to lubricants, motors and bearings. A fairly large external sun shield has been added to the AVHRR/3 scan motor housing to reduce sunlight impingement and associated calibration problems that have been briefly observed during some prior missions. Channel 3A will be time shared with the previous 3.7 μm channel, now called channel 3B.
The first half of the dynamic range for AVHRR/3 channels 1 and 2 represents 0 to 25% albedo while channel 3A has the first half of its dynamic range used for detection of albedo level changes from 0 to 12.5% albedo. These are referred to as dual slope or split gains. Previous AVHRR instruments used one linear calibration equation for each visible channel and now two are required for each visible channel. NOAA will be monitoring the dual slopes of the ramp calibrations more closely to assure that the linearity of the electronics and inflection points for the dual slopes do not change as the instrument ages or with other factors such as temperature, orbital or seasonal effects. The new visible channel ramp calibrations do not use the full dynamic range as was done previously and have been observed to change slightly as the instrument temperature changes.
The Automatic Picture Transmission (APT) user sees channel 3B as channel 6 using the wedge six grey scale modulation index.
The AMSU instruments required the addition of a new spacecraft data processing box called the AMSU Information Processor (AIP) and changes to the High Resolution Picture Transmission (HRPT), Local Area Coverage (LAC), and Global Area Coverage (GAC) formats to accommodate the new AMSU data. The AIP receives data from AMSU-A1, AMSU-A2, AMSU-B at a combined data rate of 7.2 kbps and from the TIROS Information Processor (TIP) at 8.32 kbps. The AIP generates three data streams: (1) AMSU data only which is sent to the MIRP for merging into HRPT, Local Area Coverage (LAC) or recorded HRPT, and Global Area Coverage (GAC); (2) combined AMSU/TIP sent to the spacecraft Cross-Strap Unit (XSU) for tape recording if needed; (3) AMSU/TIP for direct transmission from the XSU. The HRPT is still broadcast at the old data rate of 665.5 kbps with the new AMSU data replacing what were previously spare words. Note that if the non-redundant MIRP was to fail, it would still be possible for NOAA to obtain global sounding data. Also note that Direct Sounder Broadcast (DSB) of TIP data does not include AMSU data. DSB users will have access to HIRS/3, DCS-2, SEM-2, and SBUV/2 data as defined in the new TIP format. Most of the previously used or spare TIP words now contain DCS-2 data to satisfy the growing needs of Data Collection System (DCS) users.
The High Resolution Infrared Radiation Sounder (HIRS/3) has spectral channel changes that were made primarily to improve soundings and to be congruent with the specifications developed for the GOES-I through -M Sounders. The HIRS/3 cooler set point was decreased to approximately 100K which will improve the two infrared detectors' performance. The HIRS/3 scan profile was also changed to eliminate the viewing of the second/cold blackbody internal calibration target from the automatic calibration sequence and to use the additional time to perform another scan (38 total scans per calibration sequence) of the earth. It was cost effective to leave the second calibration target in the instrument and leave its viewing as a commandable option. The HIRS/3 instrument has been improved for longer lifetime and produces lower noise levels (better NEDN performance).
The Space Environment Monitor (SEM-2) has improved calibration and particle detection capabilities. The Total Energy Detector (TED) measures to a lower energy of 0.05 KeV and the TED integral F (ALPHA) has two ranges of 0.05 to 1 and 1 to 20 KeV. The Medium Energy Proton and Electron Detector (MEPED) has a fourth omnidirectional proton measure at 140 MeV. The MEPED has a new fixed mounting on the spacecraft and the TED has also been relocated to maximize particle detection abilities.
The Solar Backscatter Ultra Violet Spectral Radiometer (SBUV/2) has undergone relatively modest improvements. It's Programmable Read Only Memory (PROM) will be changed to a Random Access Memory (RAM) due to parts obsolescence and to provide more operational flexibility. The grating drive system has been improved to provide more torque margin. The diffuser angle was changed 9 degrees to improve the accuracy of radiometric data in the Irradiance mode. Range 3 data is provided from the PMT anode. The SBUV/2 is planned for afternoon missions only and is not presently planned for flight on NOAA-K although NOAA-K was tested with it and can be launched into either orbit.
The Data Collection System (DCS) data rate increased from 1200 to 2560 bps and the number of Data Recovery Units (DRUs) doubled from 4 to 8. DCS-2 bandwidth increased from 24 kHz to 80 kHz.
The Search and Rescue Processor (SARP-2) Data Recovery Units increased from 2 to 3 to handle more global distress messages and to better detect interfering signals. SARP output message formats are significantly different and commandable capability exists to issue pseudo messages for improved isolation of interfering signals from the ground.
Efforts have been made to improve reliability and performance while minimizing cost and impacts to users of POES satellite data. While the POES satellites may superficially appear to be production line copies, they have all been uniquely different thus far and the NOAA KLM era marks significant evolutionary and perhaps revolutionary improvements to NOAA's abilities to satisfy its multifaceted environmental monitoring and prediction missions.
|Previous Section||Top of Page||Next Section|