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SST record 50 km cell MDS
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Across-track Band Mapping Look-up Table
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LST record 50 km cell MDS
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BT/TOA Land record 17 km cell MDS
General Parameters GADS
Temperature to Radiance LUT GADS
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Infrared Histogram Test LUT GADS
11 Micron Spatial Coherence Test LUT GADS
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ATS_VC1_AX: Visible Calibration data
ATS_SST_AX: SST Retrieval Coeficients data
ATS_PC1_AX: Level-1B Processing configuration data
ATS_INS_AX: AATSR Instrument data
ATS_GC1_AX: General Calibration data
ATS_CH1_AX: Level-1B Characterization data
ATS_BRW_AX: Browse Product LUT data
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ATS_NL__0P: AATSR Level 0 product
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ATS_AST_BP: AATSR browse image
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ATS_TOA_1P: AATSR Gridded brightness temperature and reflectance
Level 2 Products
ATS_NR__2P: AATSR geophysical product (full resolution)
ATS_MET_2P: AATSR Spatially Averaged Sea Surface Temperature for Meteo Users
ATS_AR__2P: AATSR averaged geophysical product
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The AATSR Instrument
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Breakup of the Ross Ice Shelf
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Spatially Averaged Global SST, September 1993
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Special Features of AATSR
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The AATSR Handbook
SST record 17 km cell MDS
Surface Vegetation class for Land Surface Temperature Retrieval GADS
1.6 micron forward view MDS
12 micron nadir view MDS
12 micron forward view MDS
Summary Quality ADS
Surveillance Limits GADS
Master Unpacking Definition Table GADS
1.6 micron Non-Linearity Correction LUT GADS
General Parameters GADS
Thin Cirrus Test LUT GADS
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1.6 Micron Histogram
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ATS_CL1_AX: Cloud LUT data
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Summary of auxiliary data sets
Calculate Solar Angles
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ATS_TOA_1P_ADSR_sa
Visible calibration coefficients GADS
Level 1B SPH
LST record 17 km cell MDS
Conversion Parameters GADS
12 Micron Gross Cloud Test LUT GADS
ATS_PC2_AX: Level-2 Processor Configuration data
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BT/TOA Sea record 50 km cell MDS
BT/TOA Land record 50 km cell MDS
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3.1.2 Instrument Functionality

Figure3.2 below shows the functions of AATSR. In summary, AATSR operates by reflecting infrared and visible energy from either the Earth or calibration targets off the rotating Scan Mirror onto a Paraboloid Mirror. The energy is then focused and reflected into the infrared and visible Focal Plane Assemblies (FPA) where detectors convert the radiant energy into electrical signals. The low level signals from the FPA are then amplified by a Signal Pre-Amplifier (SPA) before undergoing signal processing (including digitisation) and data formatting. The data are then passed onto other systems on ENVISAT for storage and transmission back to the Earth. The next sections describe how these functions are mapped to the individual units in AATSR and section 3.1.3. discusses the instrument's internal data flow.

AATSR Functional Schematic (16K)
Figure 3.2 AATSR Functional Schematic

The functions are assigned to units and assemblies as shown in figure3.3 below.

AATSR Hardware Architecture (14K)
Figure 3.3 AATSR Hardware Architecture


The components of AATSR

Figure3.4 shows the major components of AATSR in their relative positions on ENVISAT. If ENVISAT is in flight, this is looking from the right hand side of the satellite, with ENVISAT moving from left to right in the diagram.

View of AATSR components (26K)
Figure 3.4 AATSR's Major Components and their Locations


The AATSR instrument consists of the following discrete items:

  1. The instrument itself, known as the Infrared and Visible Radiometer (IVR) 3.1.2.1.
  2. The Instrument Electronics Unit (IEU) 3.1.2.2. , providing the signal channel processing function, the scan mirror drive control and temperature sensor conditioning. The Black Body Electronics Unit (BBU) 3.1.2.2. is mounted on top, and provides the control of the black body heaters and collects temperature sensor data.
  3. The Digital Electronics Unit (DEU)/Power Conditioning and Switching Unit (PCSU)/Digital Bus Unit (DBU) 3.1.2.3. for instrument control, data formatting and power control functions.
  4. The Cooler Control Unit 3.1.2.4. which controls the Stirling cycle coolers (SCC).
  5. The Instrument Harness 3.1.2.5. , which electrically connects the above items.

These are described in more detail in the sections which follow.

3.1.2.1 Infrared and Visible Radiometer Assembly

The Flight Model IVR can be seen in figure3.5 below. This photograph shows the IVR with the thermal blankets present.

AATSR Flight Model IVR (33K)
Figure 3.5 AATSR Flight Model IVR

This view is looking up the along-track (forward view) baffle. The nadir view baffle is to the left and the two cylinders at the top and bottom of the picture between the baffles are the Black Body cavities. The baffle on the right face of the IVR is for the VISCAL.

The main features of the IVR are shown in figure1.2 in the user guide. Figure3.6 below shows an alternative view of the IVR, looking from the Earth-viewing side of the instrument.

AATSR IVR (36K)
Figure 3.6 AATSR IVR

The Infrared and Visible Radiometer is made up of a number of units:

  • The IVR structure provides physical support and mechanical interfaces for other AATSR components and ensures stable alignment for AATSR's optics. Baffles keep direct sunlight out of the IVR during normal instrument operation.

  • The Scan Mirror Unit (SMU) provides the required positioning and rotation of the Scan Mirror. The plane inclined Scan Mirror reflects the radiation from the Earth's surface or calibration sources onto the Paraboloid Mirror (figure3.8 shows the scan cycle). The control of the mechanism is performed by the Instrument Electronics Unit 3.1.2.2.1. .

  • The Paraboloid Mirror Assembly (PMA) provides the support for the off-axis paraboloid mirror and the aperture stop. The mirror focuses the reflected radiation from the Scan Mirror into the Focal Plane Assembly.

  • The Focal Plane Assembly (FPA) includes the detectors which convert the radiation into electrical signals and the optical components necessary to select the seven spectral ranges of interest. The FPA consists of two parts, one, the Infrared FPA (IRFPA), for the four infrared detectors, which are cooled to 80K, and the other, the Visible FPA (VFPA), for the three visible detectors. The VFPA is not cooled. The IRFPA contains the single field stop, which defines AATSR's Instantaneous Field of View (IFOV) for all the detectors. Details of the IFOV and AATSR's sampling around the scan are contained in section 3.2.1.2.1. .

  • The Signal Preamplifier (SPA)amplifies each of the detector signals from the FPA, before they are passed on to the Instrument Electronics Unit 3.1.2.2.1. for processing.

  • A pair of Black Body cavities (BBCs) provide a hot (at approximately 305K) and cold (at approximately 265K) calibration reference for the infrared detectors on every scan, as well as a zero radiance reference for the visible detectors. They are controlled by the Black Body Electronics unit (BBU) 3.1.2.2.2. . On AATSR, there are 6 temperature sensors on each of the BBCs, compared to the 7 on each for ATSR-1 and ATSR-2. Five of the temperature sensors are mounted on the base of the cavity, with the sixth on the wall.

  • The VISCAL unit is the "bright" calibration source for the visible channels on AATSR (one of the BBCs is used as the "dark" calibration source). The VISCAL provides an approximately 16% radiance calibration reference signal when illuminated by the sun for approximately 34 seconds once per orbit near sunrise.

  • The Cooler Mechanism Assembly provides mechanical support for, and includes, the pair of Stirling cycle coolers (SCC) which cool the IRFPA detectors. The structural attachment to the FPA is decoupled by a pair of bellows, while the thermal attachment is via a pair of flexible braids. The coolers are controlled by the Cooler Control Unit 3.1.2.4. .

  • The heat dissipated by the coolers is radiated into space by a thermal radiator, which is connected to the Cooler Mechanism Assembly by a heatpipe.

  • The IVR also has thermal hardware (i.e. multi-layer insulation blankets, temperature sensors), to ensure that the component temperatures are maintained within safe limits and that performance of the radiometer is not compromised.

  • The electrical connections between items on the IVR are provided by the IVR harness.

3.1.2.2 Instrument Electronics Unit/Black Body Electronics Unit

The radiometer electronics are contained in the Instrument Electronics Unit (IEU). The Black Body electronics (BBU) are in a separate unit which is mounted on the top of the IEU. Power and the instrument's Command and Telemetry Bus are routed through the IEU to the BBU.

3.1.2.2.1 Instrument Electronics Unit

The IEU forms a part of the electronics subsystem for the AATSR Instrument. As shown in figure3.3 , it interfaces with the Digital Electronics Unit (DEU) and Power Conditioning and Switching Unit (PCSU) 3.1.2.3. , the Signal Preamplifier (SPA), the Scan Mirror Unit (SMU), the BBU 3.1.2.2.2. , and the Infrared Visible Radiometer (IVR) 3.1.2.1. itself.

The IEU houses the electronics for processing the analogue signals from the detectors in the Focal Plane Assembly (FPA) after they have been amplified by the SPA, for temperature sensors and analogue monitors and for driving the SMU.

The interfaces to the DEU/PCSU are for the transfer of command, telemetry and science data and for the supply to the IEU of regulated power.

The electronic system in the IEU are subdivided into the sub-systems listed below:

(1) Signal Channel Processing
There are seven Signal Channel Processors (SCP) which receive the analogue inputs from the FPA's detectors after they have been amplified by the SPA. The SCPs scale and convert the analogue inputs to serial digital words. Scaling is performed under control of the DEU 3.1.2.3. 's Auto Gain/Offset and Auto Offset software.
(2) Scan Mirror Drive
The IEU includes the control system for the SMU. The performance of the SMU and its control system is described in section 3.2.1.3.2. .
(3) Temperature Sensors
The IEU conditions and digitises integrated circuit temperature sensors mounted on the instrument structure, SMU, VFPA and visible calibration target assembly. It also provides these functions for the cryogenic temperature sensors in the IRFPA.
(4) Visible Calibration Monitor
The VISCAL includes a monitor circuit which measures the radiance of the VISCAL source. The monitor output is conditioned and digitised by the IEU.

3.1.2.2.2 Black Body Electronics Unit

The Black Body electronics Unit (BBU) has the following main functions:

(1) Heater control
The BBU selects the BBC to be heated and the heater level under command of the DEU 3.1.2.3. . Only one BBC can be heated at a time and the main heater has three power settings, of which the intermediate level is normally used.
(2) Temperature Sensors
The temperature sensors (6 platinum resistance thermomeneters on each CBB and a temperature sensor in the BBU) are sampled by the BBU on request of the DEU 3.1.2.3. .

3.1.2.3 Digital Electronics Unit/Power Conditioning and Switching Unit

The Digital Electronics Unit/Power Conditioning and Switching Unit (DEU/PCSU) assembly consists of two units:

  • The DEU contains the Instrument Control Unit (ICU) function and the function to format the detector and other data from the IEU. The ICU receives telecommands from the ground via the Payload Module Computer and sends telemetry back. The ICU includes software to control the instrument as well as for monitoring housekeeping parameters for out of limits conditions. The ICU software is stored in Electrically Eraseable Programmable Read-Only Memory (EEPROM) and can be updated in flight.

    The data formatter includes the pixel selection function based on a programmable pixel map and the hardware to assemble the science data and auxiliary data to make up the instrument source packets for transmission to the spacecraft's High Speed Multiplexer. On AATSR (unlike ATSR-1 and ATSR-2), the source packet contains all 12 bits for each pixel in the Earth and calibration targets for all channels all the time. Therefore, the pixel map will not be routinely varied in flight after it has been optimised during commissioning (see section 3.2.2.1. ). The pixel map is discussed in more detail in section.

  • The assembly includes the PCSU, which provides all secondary regulated and unregulated supplies to the AATSR instrument.

The DEU interfaces to the spacecraft's Onboard Data Handling bus via the Digital Bus Unit, supplied by ESA.

3.1.2.4 Cooler Control Unit

The Cooler Control Unit (CCU) controls the two Stirling cycle coolers in response to commands from the DEU 3.1.2.3. . The CCU commands the coolers' operation and continuously monitors appropriate parameters to monitor their operation. The cooler subsystem ensures that the IRFPA detectors are maintained at a stable cryogenic temperature (80K nominally), around the orbit and over longer time periods.

3.1.2.5 Instrument Harness

The instrument harness electrically connects the AATSR assemblies. It also includes electrical bonding straps from the IVR and electronics units to the ENVISAT ground reference rail.