CEOS / IVOS Working Group 4 (use of pseudo-invariant sites)
Methodology Intercomparisons: Objectives and approach
The intercomparisons study of CEOS/IVOS WG4 focused on four methodologies making use of pseudo-invariant sites for vicarious calibration or for radiometric intercomparisons. The sensors considered in this work were medium spatial resolution sensors with multi-spectral capabilities operating in the visible to thermal infrared.
A report on the methodology intercomparisons is available here .
Time series of cloud screened TOA reflectance averaged over pre-defined regions of interest were generated for tree sites:
The sensors for which data were extracted are:
The time series of extractions covers the years: 2006 to 2009.
These data were distributed in a predefined format and constitute what is hereafter called the reference dataset.
Each participating team applied its vicarious calibration methodologies and/or sensor-to-sensor radiometric intercomparison methodologies to this reference dataset. MERIS data (2nd reprocessing) were chosen as a radiometric reference to which other sensor radiometry was compared. The comparison was carried out for each methodology and for each site using standardised statistical indicators associated to the time series of radiometric differences between MERIS and other sensors.
Reference Dataset is available: You are welcome to download the reference dataset, sensor spectral responses and a ReadMe from: [DOWNLOAD DATASET HERE]
The reference dataset is fully described in the WG4 Final Report. It was generated from three separate data sources; DIMITRI (maintained by ESA and ARGANS), SADE (CNES) and RAL. It contains:
• the mean and standard deviation of TOA reflectances over pre-defined regions of interest
• the associated viewing and solar geometries
• the associated meteorological parameters extracted
|Site||North Lat||South Lat||East Lon||West Lon||Surface Type|
The reference dataset files are provided for each sensor over each site and are space delimited text files. Each row within the file represents a different satellite observation over the ROI; different sensor views are treated as separate observations (e.g. AATSR Nadir and Forward views). The different columns of data are:
|Sensor||The name of the sensor and Processing Version|
|Processing Time||dd/mm/yyyy-hh-mm-ss (not extended, duplicate of acquisition time)|
|Site Name||The validation site name|
|meanTOArho||The mean TOA reflectance for each band (*)|
|stdevTOArho||The standard deviation of reflectance for each band (*)|
|VZA||The mean viewing zenith angle at each band (*), 0° = nadir, 90° = horizon|
|VAA||The mean viewing azimuth angle at each band (*), 0° = nadir, 90° = horizon|
|NPixels||The number of pixels within the ROI for this observation|
|Latitude||The site centre Latitude|
|Longitude||The site centre Longitude|
|SZA||The mean Solar Zenith Angle, 0° = nadir, 90° = horizon|
|SAA||The mean Solar Azimuth Angle, 0° = North, 90 = East°|
|WVAP||The mean Solar Zenith Angle, 0° = nadir, 90° = horizon|
|OZONE||The mean ozone concentration in cm atm|
|PRESS||The mean surface pressure in mbar|
|WIND||The mean wind speed modulus in m s-1|
Missing values are set as -999.
* Sensor Bands:
AATSR: all seven bands in ascending wavelength order,
MERIS: all 15 bands in ascending wavelength order
MODIS-Aqua: MODIS Band Numbers 8 - 9 - 3 - 10 - 4 - 1 - 2 - 5 - 6 – 7 (wavelengths 412 - 443 - 469 – 488 - 555 - 645 - 858 - 1240 - 1640 – 2130)
PARASOL: all bands in ascending wavelength order: 443 - 490 - 565 - 670 - 763 - 765 - 865 - 910 - 1020
VEGETATION: all four bands in ascending wavelength order