Calculate STP Elevation

Use the RPS > Calculate STP Elevation option (geogxnet.dll(Geosoft.GX.Radiometrics.CalculateSTPElevation;Run)*) to apply altimeter correction and calculate the STP Standard Temperature and Pressure equivalent elevation, adjusted for current temperature and pressure conditions. To generate STP-corrected altitude output, the process requires input from either a barometric elevation channel or a pressure channel, along with temperature and radar altimeter data. For further details, refer to the Application Notes.

Calculate STP Elevation dialog options

Method	Choose how to correct the height using standard temperature and either barometric elevation or standard pressure: Barometric altitude channel: Select this option to correct using barometric elevation. Pressure channel: Select this option to correct using standard pressure. Refer to the Application Notes for correction equations. Script Parameter: SPECTRO.STP_METHOD [0 - Barometric; 1 - Pressure]
Radar altitude channel	Select the radar altimeter channel. Script Parameter: SPECTRO.RALTRAW
Temperature channel (°C/°F)	Select the temperature channel and specify its units: °C (default) °F If the channel’s units are already defined in the Units field (right-click the channel header and select Edit to open the Edit Channel dialog) and are set to °C/C or °F/F, the unit selection updates automatically. If you choose units that do not match the channel’s defined units, a validation warning appears. Refer to the Application Notes for conversion details. Script Parameter: SPECTRO.CTEMP
Barometric altitude channel / Pressure channel (kPa/mBar)	This field is contextual: based on your method selection, either the Barometric altitude channel field or the Pressure channel field will be available. If the pressure channel method is selected, choose the pressure channel and specify its units:  kPa (default) mbar If the channel’s units are already defined in the Units field (right-click the channel header and select Edit to open the Edit Channel dialog) and are set to kPa or mbar, the unit selection updates automatically. If you choose units that do not match the channel’s defined units, a validation warning appears. Refer to the Application Notes for conversion details. Script Parameters: SPECTRO.BALTRAW SPECTRO.PRESSURE
Low-pass cutoff (fiducials)	Before converting to equivalent height at standard temperature and pressure (STP), you may need to apply light filtering to radar altimeter data to smooth out abrupt terrain changes. Enter the cutoff value to apply filtering. Default: 5 Enter 0 to skip filtering. Script Parameter: SPECTRO.RALTSWAV
Output STP altitude channel	Specify the output channel for the STP-corrected altitude. Default name: RALTSTP Script Parameter: SPECTRO.RALTSTP

Application Notes

Radiometric analysis techniques require that actual survey conditions be converted to standard atmospheric conditions. This conversion is achieved by adjusting the measured ground clearance to standard temperature and pressure (STP). The resulting STP-equivalent height represents the same mass of air, under STP conditions, between the ground and the aircraft as was present during data acquisition.

STP Correction Equations

The altitude corrected to standard temperature and pressure (STP) conditions can be calculated using one of two methods, depending on the measurement channels available.

Correction for Standard Temperature and Pressure

This method applies when direct measurements of air temperature and barometric pressure are available.

The standard reference conditions are defined as follows:

• Standard temperature: 273.15 K (0 °C), representing the freezing point of water on the Kelvin scale.

• Standard pressure: 101.325 kPa (equivalent to 101,325 Pa or 1 atm), corresponding to the average atmospheric pressure at mean sea level.

To correct the measured height to standard temperature and pressure, the STP-equivalent height is calculated using the following equation:

Correction for Standard Temperature and Barometric Elevation

The standard temperature and pressure correction described above assumes the availability of radar altimeter, air temperature, and barometric pressure measurements. However, some systems do not provide direct pressure data. In such cases, barometric altimeter readings can be used.

The STP-equivalent height is calculated as follows:

The variables used in the equations above are defined as follows:

• h_radar — Observed height above ground level (metres)

• h_baro — Barometric height above sea level (metres)

• h_STP — Equivalent height at STP (metres)

• T — Air temperature (°C)

• P — Barometric pressure (kPa)

Processing Workflow

This RPS tool performs the following processing steps:

1. Low-pass filtering of radar altimeter data

2. STP correction of altitude

After processing:

• Compare the raw and corrected data in the profile window.

• If the results are unsatisfactory, rerun the GX and adjust the processing parameters as needed.

References