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Geolocation Accuracy

Item 4.3 of the CARD4L NRB specification requires, as minimum, an estimate of the absolute location error (ALE) "as bias and standard deviation, provided in slant range/azimuth, or Northing/Easting" ceos_2021. As desired target the accuracy is less or equal 0.1 pixels radial root mean square error (rRMSE), which can be defined as:

$$RMSE_{planar} = \sqrt{RMSE_{SLC,Az}^2 + (\frac{RMSE_{SLC,Rg}}{sin(\theta_{i,min})})^2 + RMSE_{DEM,planar}^2 + RMSE_{proc}^2}$$

The error induced by the DEM can be described as:

$$RMSE_{DEM,planar} = \frac{\sigma_{DEM}}{tan(\theta_{i,min})}$$

where

θi, min = The minimum possible angle of incidence

RMSESLC, Az/Rg = Error induced by SLC source data in azimuth/range

RMSEDEM, planar = Error induced by DEM inaccuracy

RMSEproc = Error induced by other processing steps

σDEM = DEM accuracy at 1σ (LE68)

Limitations

Currently, the following simplifications need to be considered for the calculation of rRMSE values found in the metadata of each S1-NRB product:

  • Processing induced errors (RMSEproc) and the error term related to DEM interpolation are not further considered and assumed to be 0.

  • The DEM accuracy (σDEM) is estimated on the global mean accuracy LE90 reported for the COP-DEM airbus_2022 under the assumption of gaussian distribution:

    • Global: LE90 = 2.57; LE68 ≈ 1.56
  • rRMSE is only calculated if a COP-DEM was used for processing, otherwise the value is set to None

Development Status

The development status is tracked and discussed in the following Github issue: #33