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2.6.3 RA-2/MWR Level 1b product

2.6.3.1 Definition

The RA-2/MWR level 1b product contains the geolocated engineering calibrated data. When creating the L1b product, the raw Level 0 data is converted into engineering units and the relevant instruments calibration and characterisation data is applied.

Although two different products (RA2_ME__0P and MWR_NL__0P) are needed as input, only one merged RA-2/MWR product is created at Level 1b, containing the meaningful results from both the RA2 and the MWR Level 1b processing activities.

2.6.3.2 Structure

The RA-2/MWR Level 1b product is composed of an MPH and SPH (common to both instruments) and 4 Measurement Data Sets (RA2, individual echoes waveforms, RA-2 Point Target Response and MWR).

The layout of the MPH is common to all EnviSat instruments and contains information such as the first/last record time in the product, UTC/SBT time reference table, Orbit State Vector information, SPH size and total product size.

The SPH and the Data Sets are instead specific of each product and of each processing level.

The SPH cotnains information concerning the whole product, while the Measurement Data Sets contain information specific of every record.

Each MDS record includes a time record, a quality indicator flag and a record counter inside the product.

The RA2 and MWR MDSRs contain the latitude and longitude value of every record, quality fields (MCD) and the science data.

2.6.3.3 RA-2/MWR Level 1b SPH

The unique RA-2/MWR L1b SPH contains information coming from both the RA2 and MWR Level 1b processing steps.

The start/stop latitude and longitude values for RA2 and MWR records are contained in the SPH, along with the first and last record times for both instruments.

Quality flags indicating if the percentage of records with header or processing errors (for RA2) or header, telemetry and processing errors (for MWR) is less than a threshold (extracted from the auxiliary configuration files) are included.

Information like percentage of records in the different RA2 operational modes, and percentage of the RA2 records in the different Ku bandwidths appears in the L1b SPH as well.

2.6.3.4 Level 1b RA2 MDS

This RA2 Level 1b Data Set shall reflect the structure and contents of the input RA2 Level 0 Source Packets, with values converted into engineering units and all RA2 calibration and characterisation data applied.

One output record is generated for each Data Block of the Level 0 Source Packets. In other words, one output record represents one elementary measurement corresponding to about 55.7 milliseconds of data take.

Some information in these output records come from the Source Packet Header, and so, it will be repeated for the 20 records corresponding to the same ISP.

Instead. some other values are Data Block dependant, meaning that different values will be output for every L1b record of the same ISP.

The Ku/S IF mask corrected waveform samples, including the 2 DFT extra samples are included in the RA2 L1b records, along with the main output results from the AGC processing (corrected Ku abdn and S band AGC, scaling factors for sigma_0 evaluation for both bands, etc.), PTR processign (time delay and sigma_0 flight calibration factors for both bands), window delay for Ku and S, calibrated Noise Power Measurement, Doppler correction for Ku and S, Delta_Offset, etc.

 

Most of the fields in these records are meaningful only if mode_id at DB level is Tracking, Preset Tracking or Preset Loop Output. Otherwise, default values (0) are used to fill those fields in.

Nevertheless, fields like UTC time, latitude, longitude, DB number, record counter, etc., are always correctly filled in independantly of the mode of the instrument.

2.6.3.5 Level 1b RA2 individual echoes waveforms MDS

This MDS contains the unaveraged individual echoes appended to the Level 0 RA2 ISPs.

This MDS will only be present in the L1b product if there are RA2 Level 0 ISPs with individual echoes present.

These records include always a time (that corresponds to the time of the first DB of the first ISP containing individual echoes), an OBDH datation (that coincides with the OBDH value from the first ISP containing individual echoes, and that does not change for all the individual echoes waveforms records in the same sequence), a record counter, a source sequence counter (extracted from the header of the first ISP in the sequence of individual echoes) and the individual echoes themselves.

The individual echoes field contains the In-Phase and Quadrature samples, corresponding each to an 8 bit two's complement value from the Level 0 field.

2.6.3.6 Level 1b PTR MDS

This MDS consists of data output from the PTR processing operations in the Level 1b processing algorithms. The rate of these records is one every 1.114 seconds (same rate as the Level 0 RA2 ISPs, since the PTR data is included in the calibration field at the end of the ISPs).

These records include a time value, an OBDH datation word (copy of the value in the L0 ISP), a record counter, the 128 normalised PTR processed samples, the time delay and sigma_0 flight calibration factors, and some other flags.

The flight calibration factors are repeated in the main RA2 L1b MDSRs as well.

2.6.3.7 Level 1b MWR MDS

Each record in this MDS represents data coming from 8 scans of the radiometer, i.e. 1.2 seconds of data, so that it is available at a rate similar to RA2 (1.114 seconds).

No further averaging is performed when processing from L1b to L2, thus, the same record format is used for both processing levels.

In each record, datation and geolocation are included, together with some flags (MCD) to describe the validity of each output. Some instrument flags are also inserted in each record to give some information on instrument status at the acquisition time.

The fields that are filled in at Level 2, are set to 0 when outputting the L1b product.


Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry