Coordinate Systems
pyDARN offers several different measurement systems for various types of plotting: - Range Estimation: the estimate of how far the target (echo) is from the radar - Coordinate systems: Generic geographic coordinate system with conversions to AACGM and AACGM MLT
Range-Time Plots
Range Gates: RangeEstimation.RANGE_GATE a rectangle section determined by beam width and set distance for each range (nominally 45 km). RAWACF and FITACF data give their parameter values with respect to range gates. Range gates are a unit-less measure of estimating distance.
Slant Range: RangeEstimation.SLANT_RANGE is a conversion from range gates to km units. Slant range estimates the distance of ionospheric echos from the radar, using the time it takes for the radio wave to travel to the ionosphere and return, assuming the radio wave is travelling at the speed of light.
Note
Slant range is calculated from the value of frang, the distance to the first range gate. In pyDARN, we assume
that this value is the distance to the inner edge of the first range gate. We are aware that not all radars use this
exact definition, this is outside the remit of pyDARN and should be addressed at a higher level.
The value rxrise is also used in the definition of slant range. This is the receiver rise time of the radar, however,
due to discussion outside of pyDARN's remit the value of rxrise is adjusted in FITACF files and may not match
the value given in hardware files. Currently, pyDARN has decided to use the values for rxrise given in the
hardware files. We will amend or reconsider this approach as and when a solution to the differing values is found.
Ground Scatter Mapped Range: RangeEstimation.GSMR uses echos from ground scatter to adjust slant-range coordinates to be more accurate based on Dr. Bill Bristow's paper. Implemented by Dr. Nathaniel Frissell and Francis Tholley from University of Scranton. Measured in km.
Geographic Latitude (Coming Soon)
AACGM Latitude (Coming Soon)
Geographic Plots
Geographic plots include: fan, grid and convection map (coming soon) plots
Geographic: Coords.GEOGRAPHIC is the standard geographical coordinate system for latitude and longitude (degree) (coming soon)
AACGM: Coords.AACGM is Altitude Adjusted Corrected Geogmagnetic Coordinates developed by Dr. Simon Shepherd are an extension of corrected geomagnetic (CGM) coordinates that more accurately represent the actual magnetic field. In AACGM coordinates points along a given magnetic field line are given the same coordinates and thus are a better reflection of magnetic conjugacy. pyDARN uses AACGM-V2 from the aacgmv2 python library. Implemented by Dr. Daniel Billett from University of Saskatchewan.
AACGM_MLT: Coords.AACGM_MLT is Coords.AACGM with the geomagnetic longitude converted to magnetic local time
RangeEstimation methods can be used with a Coords calculation. For example, using Coords.GEOGRAPHIC and RangeEstimation.GSMR together, will give a plot of ionospheric echoes at a distance from the radar calculated in ground scatter mapped range, in geographic coordinates.
Warning
You cannot use RangeEstimation.RANGE_GATES with any Coords, the default is RangeEstimation.SLANT_RANGE