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    24-Jul-2014
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2.9.2 Level 1b processing

The auxiliary files to be used solely for the RA2/MWR L1b processing are the following:

RA2_CON_AX (RA2 Configuration file)

This file contains all thresholds and scaling factors to be used during the RA2 Level 1b processing. Some fields needed to fill in some quality information in the L1b SPH are also included in this file (i.e. thresholds to set the RA2 L1b processing and headers quality flags).

Some of the fields within this file were updated during Commissioning Phase as part of the L1b algorithms verification group activities. No future updates are foreseen.

RA2_IFF_AX (RA2 flight IF mask data)

This file contains the correction mask to be applied to the waveforms samples for the instrument IF filter shape. The IF mask may be derived on-ground or in-flight. Also, the on-ground data may differ for chain A (RA2_IFA_AX) or chain B (RA2_IFB_AX), but keeping always an identical format.

The IF flight data has been updated several times since Envisat launch.

The update is done by switching the instrument into IF Calibration mode, when 128 thermal noise samples are collected by the instrument, instead of the 128 Ku waveform samples. These samples are used on ground to estimate the IF filter shape.

The instrument is switched into this calibration mode regularly once per day, when flying over the Himalayas.

When enough IF CAL data are accumulated, and depending on the IF mask variability as function of the temperature along the orbit, a new IF Mask is created. This is done by a dedicated IECF function.

Although there is a way to select the proper IF calibration mask inside the L1b processing, (by using the altimeter measurement date, the altimeter RF subsystem chain in use and the quality flag associated to the measurement), the flight data has and will be always used for the processing.

An ESA study had shown that monthly update of the IF Mask is required. This is applied starting from cycle 42 with IPF version 5.02.

RA2_USO_AX (RA2 USO file)

This file contains the accurate estimate of the USO frequency (Tx/Rx clock period) and is updated by means of an IECF dedicated function.

Although there is a way to select the proper USO Tx/Rx clock period inside the L1b processing, (by using the altimeter measurement date, the altimeter RF subsystem chain in use and the quality flag associated to the measurement), the flight data will be used for the processing.

An update of the USO clock period format has taken place to improve the accuracy of the L1b/L2 range measurements.

MWR_SLT_AX (MWR Side Lobes Temperature file)

This file contains the side lobes contribution to the MWR brightness temperatures. There are three different algorithms that can be used to remove the effects of the secondary lobes. In the first, ERS-1 like, algorithm, the secondary lobes effects are tabled in a Side Lobe Table auxiliary file, as function of the latitude of the satellite. In the second, ERS-2 like, algorithm, instead, the side lobes contributions are obtained using the reflector physical temperatures, the transmission coefficients of the reflectors and the global side lobes contributions for each channel. The third algorithm is proposed by CLS that used one full year of ERS2 brightness temperatures to evaluate the contribution of the land emissivity (directly and after reflection by the platform) inside the measurement cell.

Two methods are available for the calculation of the side lobe contributions: ERS-1 like strategy (using a side lobe contribution table in terms of the latitude), or ERS-2 like strategy (using transmission coefficients of the reflectors for both channels, and global side lobe contributions, including cosmic background, sun and satellite contributions). Currently, the ERS-2 like method is being used for the processing of the real data.

New algorithms for the calculation of the side lobe temperature (implying a change in the aux. file format) are envisaged for a near future.

MWR_CHD_AX (MWR Characterisation file)

This file includes all the radio frequency front-end relevant parameters such as switching assembly insertion losses, hot load mismatching, cold (sky horn) chain characterisation, IF gain characteristics in terms of linearity, variation in temperature, noise figures, stability and sensitivity measurements, etc. In particular, the data in the 4 Data Sets in this file contains: thermistor polynomial coefficients to be used to evaluate the temperature of the 32 on-board thermistors by their telemetry (1st DS), expected maximum and minimum limits in temperature of the most significant thermistors, for 24 GHz and 36 GHz channels (2nd DS), linear and quadratic coefficients of the receiver gain response as a function of on-board temperature, for 24 GHz and 36 GHz channels (3rd DS) and characterisation parameters of 24 GHz and 36 GHz channels for five different reference temperatures (0�C, 10�C, 20�C, 30�C, 40�C) and for the two modes of operation (nominal and redundant).

Data from this file was updated during Commissioning Phase in the frame of the MWR cal/val group activities. No further updates are foreseen.

MWR_CON_AX (MWR Configuration file)

This file contains data used to configure the MWR processor (e.g. moving window size for the calculation of the Gain and offset temperatures, or pointing configuration for the forward and backward channels).

Data from this file was updated during Commissioning Phase in the frame of the MWR cal/val group activities. No further updates are foreseen.


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