Aquarius Level 0-to-1A Processing

1
Aquarius Level 0-to-1A Processing

• Rule 1 save everything from the Level 0 data.
• Rule 2 never forget Rule 1!
• The objective is to ensure that the Level 0-to-1A
  conversion is fully reversible.

2
Level-0 File Overview

• A single copy of the contents Aquarius memory at
  the time of the downlink, in time order, as
  generated by the Aquarius preprocessor.
• Data consist of binary science blocks spanning a
  period of 14 hours (110 Mbytes).

3
Science Block Structure
4
Radiometer Block
5
Scatterometer Block
6
Level-1A Product Overview

• Level-1A data consists of unpacked, unconverted
  science data and instrument housekeeping
  telemetry, with navigation and required
  spacecraft telemetry.
• Each file contains 1 orbit (starting at South
  Pole crossing) plus 10 minutes at each end.
• Level-1A products are formatted using HDF5
• Machine-independent, hierarchical, self
  describing format
• Attributes contain descriptive information about
  the entire file or individual objects within the
  file
• Groups provide logical association and hierarchy
• Data objects are multidimensional arrays of
  standards types

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Level-1A Product Elements

• Product metadata, i.e., descriptive information
  about the entire file (e.g., sensor, time,
  quality)
• Data characteristics (number of blocks, etc.)
• Science block metadata (time and quality)
• Raw sensor data
• Block header elements
• Housekeeping telemetry by subsystem
• Radiometer and scatterometer science data,
• Navigation data (original sampling rate)
• Orbit vectors from predicted or definitive
  ephemeris
• Attitude data from SAC-D telemetry
• Unpacked and converted Aquarius housekeeping
  telemetry
• SAC-D housekeeping telemetry (selected fields
  converted)

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Level 0-to-1A Mapping
Synch and Time Tag
Aquarius Raw Telemetry
Scatterometer science data Header Power Loopback D
C
Radiometer science data Header Short
Accumulations Long Accumulations
Checksum
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Level-1A Ancillary Data

• Orbit ephemeris data provided by CONAE
• Predictive ephemeris for near-real-time
  processing
• Definitive ephemeris for refined processing
• GPS data from SAC-D as backup
• Attitude data from SAC-D housekeeping telemetry
• Additional SAC-D housekeeping telemetry provided
  by CONAE from downlink data

10
Calibration and Orbit Adjust Data

• Cold sky calibration and orbit adjust periods
  will be identified during Level-1A processing,
  either from the command schedule or the
  spacecraft housekeeping telemetry.
• Data from these periods (plus additional data as
  needed for stabilization, TBD) will be written to
  separate files and excluded from downstream
  processing.
• Calibration files will be provided for offline
  analysis.

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Level-1A Format Examples

• 3.1 Mission and Documentation
• Product Name (character) the name of the product
  file (without path).
• Title (character) "Aquarius Level-1A Data".
• Data Center (character) "NASA/GSFC Aquarius Data
  Processing Center".
• Mission (character) "SAC-D Aquarius".
• Mission Characteristics (character) "Nominal
  orbit inclination 98.0 (Sun-synchronous) node
  6 PM (ascending) eccentricity lt0.002
  altitude 650 km ground speed 6.825 km/sec".
• Sensor (character) "Aquarius".
• Data Type (character) "SCI, CAL or DMP.
• Software ID (character) identifies version of
  the operational software used to create this
  product.
• Processing Time (character) local time of
  generation of this product concatenated digits
  for year, day-of-year, hours, minutes, seconds,
  and fraction of seconds in the format of
  YYYYDDDHHMMSSFFF.
• Input Files (character) the name of the Level-0
  file(s) (without path) from which the current
  product was created. This information is stored
  in the product as part of its processing history.
• Processing Control (character) all input and
  processing control parameters used by the calling
  program to generate the product. Vertical bars
  or carriage return characters serve as parameter
  information delimiters. This information is
  stored in the product as part of its processing
  history.

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Level-1A Format Examples (cont.)

• 4.2.3 Raw Radiometer Science Data
• radiom_header (2-byte integer, array size Number
  of Blocks) long_name Radiometer block
  header" this header specifies the packet type
  (standard or memory dump) and the housekeeping
  telemetry packet number (0 through 3).
• radiom_savg (2-byte integer, array size Number of
  Blocks x Radiometer Subcycles x Radiometer Short
  Accumulations x Radiometer Channels) long_name
  Radiometer Short Accumulations radiometer data
  accumulated and averaged within a subcycle.
• radiom_lavg (2-byte integer, array size Number of
  Blocks x Radiometer Long Accumulations x
  Radiometer Channels) long_name Radiometer
  Long Accumulations radiometer data accumulated
  and averaged over multiple subcycles within a
  block.
• 4.2.4 Raw Scatterometer Science Data
• scatter_headers (byte, array size Number of
  Blocks x Scatterometer Subcycles) long_name
  Scatterometer subcycle headers headers for
  each scatterometer subcycle within a block.
• scatter_pwr (2-byte integer, array size Number of
  Blocks x Scatterometer Subcycles x Scatterometer
  Channels) long_name Scatterometer Power raw
  scatterometer power data for each subcycle within
  a block.
• scatter_loop (2-byte integer, array size Number
  of Blocks x Scatterometer Channels) long_name
  Scatterometer Loopback Measurements
  scatterometer loopback data average over the
  subcycles within a block.
• scatter_dc (2-byte integer, array size Number of
  Blocks x 2) long_name Scatterometer DC data
  raw scatterometer DC data averaged over the
  subcycles within a block.

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Aquarius Telemetry Example
14
Aquarius Level-1A Merge

• Multiple versions of Level-1A products will be
  generated for each orbit from overlapping periods
  in successive Level-0 files.
• Level-1A merge processing will consolidate these
  into a single product by selecting the best
  quality data for each science block using TBD
  metrics.

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Aquarius Level-1B Products

• Separate files for radiometer and scatterometer.
• Formatted using HDF5
• Product-level metadata is essentially the same as
  for Level 1A.
• Calibrated science data, processing information
  and quality indicators as defined for each data
  type, per beam and polarization.
• Navigation and geolocation data at block or
  subcycle times.

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Radiometer Level-1B Science Data

• Calibrated brightness temperatures (per subcycle)
• Noise temperatures (per block)
• Voltage offsets (per block)
• Gains (per block)
• RFI flags (per subcycle)
• Brightness temperatures RMS (per subcycle)

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Scatterometer Level-1B Science Data

• Sigma0 (backscatter)
• KPC (normalized standard deviation)
• Signal-to-noise ratio
• Noise value
• All fields generated per subcycle

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Level-1B Navigation Data

• Orbit position and velocity (per block)
• Attitude roll, pitch and yaw angles (per block)
• Beam center latitude/longitude (per beam and
  subcycle)
• Beam edge latitude/longitude (ellipse major and
  minor axes) (per beam and block)
• Incidence and azimuth angles (per beam and block)
• Polarization roll (per beam and block)
• Doppler shift (per beam and block)

19
Pointing Knowledge Assessment

• Pointing knowledge requirement is 0.1 degree 3
  sigma, driven primarily by the radiometer
  sensitivity to the incidence angle.
• This is equivalent to about 2 km of location
  accuracy at the surface.
• Verifying this level of accuracy could be
  challenging with the Aquarius beam size.
• Overlap with land surfaces should be useful, but
  approach needs to be developed.
• This will most likely be performed as a separate
  processing step after Level-1B processing.

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Pointing Knowledge Assessment (cont.)

• What is the expected sensitivity of the
  radiometer signal to land vs. ocean surface?
• How does this vary with surface type?
• Is surface elevation a factor?
• How is polarization affected?
• Will the sensitivity and coverage be sufficient
  to characterize systematic as well as static
  errors?
• How can the method be designed to process a
  reasonable minimum subset of the radiometer data
  (60,000 blocks, 720,000 subcycles) per day?
• Does the scatterometer provide an independent
  assessment?