NOAA KLM User's Guide Section 4.1

Introduction Page, NOAA KLM TOC, Acronyms
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4.1 HRPT System

4.1.1 General

The High Resolution Picture Transmission (HRPT) system provides data from all spacecraft instruments at a rate of 665,400 bps. The S-band realtime transmission consists of the digitized unprocessed output of five AVHRR/3 channels, plus the TIP (HIRS/3 for NOAA KLM and HIRS/4 on NOAA-N, -N', SBUV/2, SEM, DCS/2) data and AMSU data. All information necessary to calibrate the instrument outputs is included in the data stream.

During NOAA-K activation and evaluation, it was determined that AMSU-A channels 7 and 15 were switched. This switch should be transparent to Level 1b users as the channels were corrected (switched back) by the ingest software, however, direct readout users should be aware of this problem. Only the radiometric data was affected, the housekeeping temperatures of channels 15 and 7 oscillators are correct as they are now. The antenna patterns, beam efficiency and beam widths are correct as they were not affected by the switch. Band pass for channels 7 and 15 was not affected due to extremely broad rf-detectors.

4.1.2 Transmission Characteristics

The S-band transmission of time multiplexed, digital data is in a split phase format. For NOAA KLM, split phase data "0" is defined as being +68 degrees phase during the first half of the bit period and -68 degrees during the second half of the bit period. The split phase data "1" is defined as being -68 degrees phase during the first half of the bit period and +68 degrees phase during the second half of the bit period, for NOAA KLM. Note, the NOAA-N,-N' satellites have a slightly different phase angle (see Table 4.1.2-2). Table 4.1.2-1 shows the general characteristics of the HRPT transmission system, while the general HRPT parameters for both NOAA KLM and NOAA-N,-N' are shown in Table 4.1.2-2.

4.1.3 HRPT Minor Frame Format

The MIRP outputs the HRPT format simultaneously with the Automatic Picture Transmission (APT), Global Area Coverage (GAC) and Local Area Coverage (LAC) formats. GAC and LAC data are not considered real time, as these data are stored on the spacecraft digital recorders for readout by the CDA stations. The HRPT data format consists of a major frame which is subdivided into three minor frames.

Of special note is the flag in the telemetry (Word 7, Bit 10) which will indicate which of AVHRR/3 channel 3 sensors (3A or 3B) is operating. When channel 3B is selected, the patch temperature data is output every scan line (during the backscan), and every other scan line when channel 3A is selected. The data output will switch instantaneously between 3A or 3B upon command, even if the scan is in the middle of a line. However, the way the flag operates there is one scan line of uncertainty when switching from 3B to 3A, and two lines of uncertainty when switching from 3A to 3B.

4.1.3.1 HRPT Minor Frame Format for NOAA KLM

On NOAA KLM, TIP and AMSU data are updated at the major frame rate. That is, the three minor frames which make up the major frame will contain TIP data in the first minor frame, backfill in the second minor frame, and AMSU data from the AIP, in the third minor frame. In the previous series of satellites (NOAA E-J), the major frame consisted of three minor frames of only the TIP data. The details of the HRPT, AIP, and TIP minor frame formats for NOAA KLM are shown in Tables 4.1.3.1-1, 4.1.5.1-1 and 4.3.3.1-1, respectively.

Table 4.1.3.1-1 describes the minor frame format for HRPT on the NOAA KLM satellites.

4.1.3.2 HRPT Minor Frame Format for NOAA-N,-N'

On NOAA-N,-N', the HRPT format provides a major frame, which is made up of three minor frames. TIP and AMSU/MHS data are updated at the major frame rate. That is, the three minor frames, which make up a major frame, will contain TIP data in the first minor frame, backfill in the second minor frame, and AMSU/MHS data in the third minor frame. The HRPT is provided in a split phase format to the S-Band Transmitter. The S-band transmission of time multiplexed, digital data is in a split phase format. The split phase data "0" is defined as being +67 phase during the first half of the bit period and -67 phase during the second half of the bit period. The split phase data "1" is defined as being -67 phase during the first half of the bit period and +67 during the second half of the bit period. The time code contained in each minor frame indicates the spacecraft time 1.13 ± 0.5 milliseconds before the beginning of bit 1 of word 1. The HRPT minor frame format for NOAA-N,-N' is shown in Table 4.1.3.2-1.

4.1.4 Digital "A" Telemetry

The output data signals supplied by the instrument to the spacecraft can be assigned to three categories: 1) instrument Digital "A" (scientific) data; 2) Digital "B" Telemetry; and 3) Analog Telemetry. For purposes of this document, Digital "A" data only are described in this section.

4.1.4.1 AMSU-A1 for NOAA KLM and NOAA-N,N'

The AMSU-A1 Digital "A" telemetry incorporates all of the radiometric data taken during one scan. It also includes the data from the on-orbit calibrations. In the Full Scan Mode, the AMSU-A1 for NOAA KLM and NOAA-N,N' has 1,244 Digital "A" telemetry points, as identified in Table 4.1.4.1-1.

Note: For S/N 103 (flown on NOAA-15) only, all scene positions, warm calibration and cold calibration, channel 7 and channel 15 radiometric data are interchanged; i.e., channel 7 radiometric output is actually channel 15, and channel 15 is actually channel 7.

Table 4.1.4.1-2 gives more details on the AMSU-A1 housekeeping data which are stored in Bytes 5-8 and also the temperature sensor data (bytes 1089-1178).

4.1.4.2 AMSU-A2 for NOAA KLM and NOAA-N, N'

The AMSU-A2 Digital "A" telemetry incorporates all of the radiometric data taken during one scan. It also includes the data from the on-orbit calibrations. The AMSU-A2 has 316 Digital "A" telemetry points, as described in Table 4.1.4.2-1, in the Full Scan Mode.

Table 4.1.4.2-2 gives more details on the AMSU-A2 housekeeping data which are stored in Bytes 5-8 and also the temperature sensor data (bytes 261-298).

4.1.4.3 AMSU-B Telemetry Data for NOAA KLM

Digital Data is clocked into the spacecraft AIP at a 16.64 kbps rate by the shift pulse whenever the Data Enable Pulse is presented to the instrument. The AMSU-B data is in the AIP minor frame words 48 through 97. The AIP reads the digital data output from the AMSU-B in 16 bit words.

The AMSU-B telemetry format consists of 78 minor frames of data. Minor frames 1 and 80 in each 8 second cycle are blank: i.e., no data is available in the PEU digital data FIFO during the first and last minor frames of each 8 second format. The 78 minor frames are organized as three blocks of 650 words as follows (representing one scan of the instrument):

36 spare words

540 words of Earth view pixel data

(90 x (5 channels + shaft position at mid-pixel))

26 words of housekeeping data

48 words of space view and target view data

(2 x 4 x (5 channels + shaft position))

This structure is maintained for all modes. In static modes, all pixel data locations contain the pixel data for the current antenna position.

The AMSU-B digital format is synchronized to the 8 second synchronization pulse. During each minor frame, 25 words of data are available in the PEU O/P FIFO within 16.7 milliseconds of the start of the minor frame (except in minor frames 1 and 80). Table 4.1.4.3-1 shows the AMSU-B digital data format.

Word Length: 16 bits

Serial Output: 25 - 16 bit words per 100 msec (MSB first)

Table 4.1.4.3-3 describes the AMSU-B digital sub-multiplexed channels.

4.1.4.4 MHS for NOAA-N,-N'

The Microwave Humidity Sounder (MHS) instrument replaced the AMSU-B instrument on NOAA-N and -N'. Scientifically, the MHS is very similar to the AMSU-B instrument, but the manner in which the data are output is quite different. The equivalent of "Digital" data on AMSU-B is referred to as "science data telemetry", or just "science data", for the MHS instrument and comes packaged in a "science data telemetry packet" or "Science Packet" (SCI PKT) for short.

The NOAA-N,N' MHS instrument science data will be delayed by two scan lines (or 5 2/3 seconds). The operational Level 1b data accounts for the delay and provides correct geo-location information. The delay, however, is not accounted for in the HRPT broadcast. The two scan line delay is caused by data buffering within the MHS instrument and the spacecraft data handling subsystem.

Consultative Committee for Space Data Systems (CCSDS) is composed of space agencies and industrial associates worldwide, working together to provide well-engineered, standardized solutions for common space data handling needs. The benefits of using CCSDS include: reduced cost, risk and development time, as well as enhanced interoperability and cross-support. For more information on CCSDS, refer to their website at: http://www.ccsds.org/. The data packets for MHS are in CCSDS format (i.e., a primary header, secondary header and checksum).

The MHS instrument, and its associated interface unit (the MIU) on the NOAA satellites, can operate in a variety of different modes and output several different packets, or formats, of data. There are nine different modes for the MHS (see Table 4.1.4.4-1 for details). In addition, all the MHS output must be funneled through a new processor, the MHS Interface Unit (MIU), which may ignore the MHS data completely and output its own telemetry instead. Depending on what mode the MIU is in, different information will be output. For purposes of this Users Guide, only the modes in which MHS data are output will be documented.

To determine what mode the MIU is in, the user must look at word 6 and the first half of word 7 of the AIP minor frame (see Table 4.1.5.2-1). If the MHS instrument is in bootstrap mode, then word 6 and the first 4 bits of word 7 contain three constant bit patterns (2 sync codes and an ID). Otherwise, the mode is found in bits 2-4 of word 6 (see Table 4.1.4.4-2), with one caveat. If the "TIP engineering frame enabled" flag (bit 5 of word 6) is set (1), then ignore bits 2-4. The MIU is in TIP engineering mode and these bits have no meaning. If the MIU is not in TIP engineering mode, then bits 2-4 of word 6 should be used.

There are MIU/MHS data in bytes 6-7 of each minor frame as well as bytes 48-97 (the normal MHS data, when available), bytes 98-101 and byte 205. Sections 4.1.5.1 and 4.1.5.2 contain the formats of the AIP minor frame, while Sections 4.3.3.1 and 4.3.3.2 contain the formats of the minor frame for TIP.

The MHS instrument only interfaces to the MIU box. The MIU interfaces to the rest of the NOAA-N, N' spacecraft through the TIROS Command and Control Subsystem (CCS), the TIROS Data Handling Subsystem (DHS) and the TIROS Electrical Power Subsystem (EPS).

The EPS portion interfacing to the MIU is the Power Subsystem Electronics (PSE) consisting of the 28 v Bus Main, Pulse Load, and Survival Buses. All power is distributed to the MHS through the MIU. The AMSU Information Processor (AIP), the Cross-Strapping Unit (XSU) and the TIROS Information Processor (TIP) boxes comprise the DHS part, while the Control Interface Unit (CIU) is the CCS interface portion of the MIU unit. All of these boxes utilize legacy bus architecture interfaces to the MIU while the MIU implements a MIL-STD-1553B redundant interface to the MHS instrument. A single 1553 bus is used for commanding (CMD), housekeeping (HK) telemetry and for science (SCI) data telemetry packets between the MHS and the MIU. However, the MIU, being the bus controller, determines whether the primary or redundant 1553 bus is utilized. Other than the 1553 bus, there is no redundancy in the MIU. The MHS is redundant internally, having both A and B sides to its electronics. The MIU supplies telemetry (MHS and MIU) to the ground during all operational modes. It also provides MHS survival temperature telemetry to the TIP even when the MHS and MIU are not powered.

The AIP provides a serial data stream from the spacecraft, which may be transmitted to the ground or embedded into other composite data streams. Within the AIP data, information is collected from the TIP, AMSU-A1, AMSU-A2, and the MIU. The TIP controls the basic data frame timing, generating a minor frame every tenth of a second (in Orbit Mode) and repeating the entire sequence every 32 seconds, called a major frame. The AIP is synchronized to the TIP timing using the 32-second major frame synch, and the harmonically related one-tenth second (10 Hz) pulse. The AIP itself has an 8-second major frame, which means it repeats its sequence four times during a TIP major frame.

Since the TIP and AIP minor frames are both 10 Hz, they are locked together, using the TIP synch timing. The TIP 32-second major frame pulse synchronizes the AIP. AIP generates its own 8-second timing, but since that period is harmonically related, it will not drift significantly from the 32-second pulse. AIP keeps the data from the AMSU's and MIU synchronized by passing on the timing pulses as appropriate.

The AIP stores the data from all four inputs in serial buffers during one minor frame, and sequences it into the data stream in the subsequent frame. This is mechanized using two sets of alternate buffers. AIP will initiate the data transfer with the 10 Hz synch, followed by the appropriate number of word strobes, 56 in the case of the MIU. The synch serves only to define the start of the transfer. The actual timing of the strobes will differ for each data source, and in the case of the MIU may not even be continuous, but it will always follow the synch.

The MIU provides a total of 80 sets of 56 8-bit words, called minor cycles, each of which will be inserted in an AIP minor frame. A minor cycle counter within the MIU keeps track of the frame sequence, and its content is included in the 56-word data sequence. Because of the double buffer arrangement, the MIU minor cycle count may not agree exactly with the AIP minor frame. However, the 8-second synch pulse will ensure that they are sequencing together uniformly, counting the same 80 frames.

The 56-word count is synchronized using the 10 Hz pulse, so that the first word will be transferred by the strobe following the synch. The data from the MHS is partially synchronized to the TIP timing, but the MS-1553 interface bus and MHS scanning mechanics prevent an exact match. Therefore, the MIU receives the MHS data packets, and packages them along with housekeeping telemetry, to produce the 56-word AIP data.

The 10 Hz and the 8-second synch pulses are received at the MIU and applied to the software using two discrete interrupts. Although both signals are intended to be continuous over long periods, a change in system clocking may result in a jump in either one, which causes it to be early or late with respect to previous pulse timing. The MIU is expected to resynchronize itself to the new sequence.

All AIP telemetry includes the Telemetry Frame Header data in words 6-7 of every minor frame. This is the same data and format as in the TIP Telemetry described in Table 4.1.4.4-5. Table 4.1.4.4-2 contains the format of the MIU AIP data for bytes 6-7.

MIU Normal Mode (as well as slow dump, very slow dump and TIP engineering modes) telemetry is included in AIP bytes 48-97. Science Data is organized by minor frame as depicted in Table 4.1.4.4-3. Table 4.1.4.4-4 provides more details of the information in Table 4.1.4.4-3.

Table 4.1.4.4-3 contains the MIU AIP data for bytes 48-97 (the normal, slow dump, very slow dump, and TIP engineering telemetry modes).

Table 4.1.4.4-5 depicts the data