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    24-Jul-2014
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SST record 50 km cell MDS
BT/TOA Sea record 17 km cell MDS
ATS_TOA_1P_MDSR_conf
ATS_TOA_1P_MDSR_cl
ATS_TOA_1P_ADSR_pix
ATS_SST_AX_GADSR
Vegetation fraction for Land Surface Temperature Retrieval GADS
Topographic Variance data for Land Surface Temperature Retrieval GADS
Land Surface Temperature retrieval coefficients GADS
General Parameters for Land Surface Temperature Retrieval GADS
Climatology Variance Data for Land Surface Temperature Retrieval GADS
Level 0 SPH
Level 0 MDSR
Auxilliary Data SPH with N = 1
1.6 micron nadir view MDS
Summary Quality ADS
Scan pixel x and y ADS
Grid pixel latitude and longtitude topographic corrections ADS
Across-track Band Mapping Look-up Table
Configuration Data GADS
Processor configuration GADS
LST record 50 km cell MDS
Distributed product MDS
Level 2 SPH
SPH
10-arcminute mds
Limits GADS
Validation Parameters GADS
BT/TOA Land record 17 km cell MDS
General Parameters GADS
Temperature to Radiance LUT GADS
Radiance to Brightness Temperature LUT GADS
Medium/High Level Test LUT GADS
Infrared Histogram Test LUT GADS
11 Micron Spatial Coherence Test LUT GADS
11/3.7 Micron Nadir/Forward Test LUT GADS
11/12 Micron Nadir/Forward Test LUT GADS
Characterisation GADS
Browse Day_Time Colour LUT GADS
Browse SPH
Grid pixel latitude and longtitude topographic correction ADS
Level 2 SPH
Auxilliary Products
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
Level 0 Products
ATS_NL__0P: AATSR Level 0 product
Browse Products
ATS_AST_BP: AATSR browse image
Level 1 Products
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
Frequently Asked Questions
The AATSR Instrument
Instrument Characteristics and Performance
In-flight performance verification
Instrument Description
Internal Data Flow
Instrument Functionality
AATSR Products and Algorithms
Common Auxiliary data sets
Auxiliary Data Sets for Level 2 processing
Instrument Specific Topics
Level 2 Products
Level 1B Products and Algorithms
Level 1B Products
Algorithms
Instrument Pixel Geolocation
Availability
The Level 0 Product
Differences Between ATSR-2 and AATSR Source Packets
Definitions and Conventions
Conventions
Organisation of Products
Relationship Between AATSR and ATSR Products
AATSR Product Organisation
Data Handling Cookbook
Characterisation and Calibration
Monitoring of AATSR VISCAL Parameters
Latency, Throughput and Data Volume
Throughput
Introduction
Heritage
Data Processing Software
Data Processing Centres
The AATSR Products User Guide
Image Gallery
Breakup of the Ross Ice Shelf
Land cover in the Middle East
Typhoon Saomai
Mutsu Bay, Japan
Deforestation in Brazil
Spatially Averaged Global SST, September 1993
Further Reading
How to use AATSR data
Why Choose AATSR Data?
Why Choose AATSR Data?
Special Features of AATSR
Principles of Measurement
Scientific Background
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
Fog/low Stratus Test LUT GADS
1.6 Micron Histogram
Browse MDS
ATS_CL1_AX: Cloud LUT data
Glossary
Pre-flight characteristics and expected performance
Payload description, position on the platform
Auxiliary products
Auxiliary Data Sets for Level 1B processing
Summary of auxiliary data sets
Calculate Solar Angles
Image Pixel Geolocation
Level 0 Products
Acquisition and On-Board Data Processing
Product Evolution History
Hints and Algorithms for Higher Level Processing
Data Volume
Software tools
Summary of Applications vs Products
Geophysical Coverage
Geophysical Measurements
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
Level 2 Products
Hints and Algorithms for Data Use
BT/TOA Sea record 50 km cell MDS
BT/TOA Land record 50 km cell MDS
Level 2 Algorithms
Signal Calibration
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1.1.3 Principles of Measurement

The key measurement principles of the AATSR instrument are outlined below. Detailed information on the AATSR instrument can also be found in Section(Chapter 3. ), The AATSR Instrument, of the Reference Guide.

1.1.3.1 The AATSR Instrument

The (A)ATSR instruments are unique in their use of along track scanning to provide two views of the surface and thus improve atmospheric correction. The surface is first viewed along the direction of the orbit track, at an angle of 55°, as the spacecraft flies towards the scene. Then, 150 seconds later, or when the satellite has moved approximately 1000 km forward along the ground track, a second observation is made of the same scene at the sub-satellite point, as shown in Figure1.1 .

image
Figure 1.1 AATSR Viewing Geometry

The AATSR dual view is also described in more detail in Section 1.1.5. of this User Guide, on the Special Features of AATSR, with the geometry and pointing performance discussed in Section 3.2.1.3. of the Reference Guide.

The AATSR instrument itself is shown in Figure1.2 .

image
Figure 1.2 Main Features of the AATSR Instrument

In operation, infrared and visible energy is reflected off a Scan Mirror mounted on the Scan Mechanism onto a Paraboloid Mirror. From this 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 amplified, digitised formatted and passed onto other systems on the satellite to transmit them back to the Earth.

AATSR employs a pair of closed-cycle mechanical coolers to maintain the thermal environment necessary for optimal operation of the infrared detectors. The FPA for the thermal infrared wavelength region is cooled to about 80 K whilst the FPA for the visible channels is maintained at ambient temperature.

In addition to the Earth view, the AATSR detectors also view calibration targets for the visible and thermal channels during each circular scan. Two stable high-accuracy blackbody targets provide calibration of the IR channels for every scan, whilst an on-board visible calibration system (VISCAL) is viewed once per orbit.

Further information on the AATSR coolers and on-board calibration systems can also be found in Section 1.1.5. on the Special Features of AATSR.

1.1.3.2 AATSR Flight Operations

Information about the current and past status of the AATSR instrument and its performance is provided via the AATSR Operations website.

Modes

AATSR has a single operational mode, MEASUREMENT mode, for nominal routine operations. The only routine interruption to the data flow will occur when the cooled detectors are warmed up to ambient temperature to remove condensation that may have been deposited at low temperatures (a process known as outgassing).

Outgassing

Contaminants from the satellite continually condense onto the cold surfaces of the FPA and its detectors. This degrades instrument operation due to signal attenuation, and because the changed surface emissivities increase the radiative load on the cooler. Signal calibration is not affected by this phenomenon, as the view of the calibration targets is subject to the same modification as the Earth view. Nevertheless, occasionally the FPA is allowed to warm up to remove these contaminants.

Outgassing periods last about 2 days and occur at intervals of approximately 3 months. Information about such outgassing events is made available to users in advance on the AATSR Engineering Data System web site, accessible from the AATSR Operations website.

No useful thermal channel data are collected during these periods.

The operation of the visible detectors is unaffected by this warming, although care must be taken when using visible channel data acquired at this time. The 1.6um channel data is absent when the infrared FPA is warm, therefore the Flight Operations Support team are unable to generate daily ATS_VC1_AX files and there are no corresponding deliveries to the PDS.

Following an outgassing, for optimum calibration the supply of VC1 files once per orbit, rather than once per day, is recommended for approximately three weeks afterwards. The current FOS system is not designed to provide files at this frequency. Therefore, when the delivery of daily ATS_VC1_AX files resumes, the calibration of visible channel data acquired during this period is still considered to be sub-optimal.

A tool to provide VC1 files once per orbit for consolidated data processed off-line may be introduced in the future.

Low-Gain Configuration

It is possible to switch the 11 and 12 µm channels into a low-gain configuration, to facilitate the monitoring of 'hot' areas, however this can be done within MEASUREMENT mode, without the need to interrupt normal operations. The low-gain command applies for a number of scans in the range 1-1024, selectable by macrocommand. Data from the other 5 channels will be acquired as normal during this period. This function will only be used over large bodies of land, in order to preserve the primary mission objective of global SST retrieval. Use of this function will be restricted for the first few months of AATSR operation to allow for testing and improved configuration. Any operational use of this mode will be authorised by the AATSR Quality Working Group on a case by case basis.

Data Availability

Data from all of AATSR's channels will be available all of the time at full 12-bit digitisation. The improvements between ATSR-2 and AATSR in this respect are once again elaborated in section 1.1.5.4. , Special Features of AATSR.

Data from AATSR will be acquired globally, on a continuous basis, and stored on-board for subsequent transmission to the ground.