Satellite scan position

Satellite scan lines are often resampled as part of the pre-processing. This is usual to reduce the number of observations processed but can be because averaging is applied over multiple fields of view to reduce the observation noise. In most processing it is neccessary to have scan positions which are increasing by one across the scan line.

Transform: RemapScanPosition

- filter: Variable Transforms
  Transform: RemapScanPosition

Parameters

This transform requires the following variable:

• sensor scan position (MetaData/sensorScanPosition)

There is one optional parameter that can be used with this variable transform and that is number of fields of view which has a default value of 3. The number of fields of view specifies the denominator when calculating the remapped scan position. See the method section below for details of how this is applied.

An example with IASI data where a value of 4 is used for the number of fields of view and the valid data only flag from the base class is used is shown below.

- filter: Variable Transforms
  Transform: RemapScanPosition
  UseValidDataOnly: true
  number of fields of view: 4

Method

The updated scan position (scan_position_new) is calculated using the following calculation.

scan_position_new = round down (sensorScanPosition / number of fields of view)

where the the part in brackets is treated as floating point division which is then rounded down to the nearest integer value. scan_position_new is written back to MetaData/sensorScanPosition.