Difference between revisions of "Standard Names For Satellite Observations"

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==Instruments or Sensors?==
 
==Instruments or Sensors?==
There is some uncertainty about the hierarchy required to completely describe devices that are used to collect data in the field. This uncertainty boils down to whether this hierarchy requires two levels, i.e. platform and instrument, or three levels, i.e. platform, instrument, and sensor. The simple hierarchy works well in many cases, but there are also clear cases that require three levels, i.e. "instruments" that host multiple "sensors".
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There is some uncertainty about the hierarchy required to completely describe devices that are used to collect data in the field. This uncertainty boils down to whether this hierarchy requires two levels, i.e. platform and instrument, or three levels, i.e. platform, instrument, and sensor. The simple hierarchy works well in many cases, but there are also clear cases that require three levels, i.e. "platform" that has "instruments" that host multiple "sensors".
  
 
Various communities have adopted conventional approaches to this nomenclature:
 
Various communities have adopted conventional approaches to this nomenclature:

Revision as of 11:00, February 20, 2013

The Climate and Forecast (CF) metadata convention maintains a list of standard names for data stored in variables of a netCDF file. Not many standard names in that list are relevant to satellite observation data so additional names are proposed here. The new names and accompanying information will follow the CF guidelines.

Instruments or Sensors?

There is some uncertainty about the hierarchy required to completely describe devices that are used to collect data in the field. This uncertainty boils down to whether this hierarchy requires two levels, i.e. platform and instrument, or three levels, i.e. platform, instrument, and sensor. The simple hierarchy works well in many cases, but there are also clear cases that require three levels, i.e. "platform" that has "instruments" that host multiple "sensors".

Various communities have adopted conventional approaches to this nomenclature:

  • GOES-R ncml examples use global attributes "platform_ID" and "instrument_ID" and metadata variables "gcmd_platform_keywords" and "gcmd_instrument_keywords".
  • The NESDIS STAR netCDF template uses global attributes "satellite_name" and "instrument_name"
  • The GHRSST data specification uses global attributes "platform" and "sensor"
  • NPP (HDF) uses global attributes "Platform" and "Instrument"

Of course agreement is more important than justification in this case. We propose to use sensor in these names because it works in the two level case and does not preclude the use of three levels when required.

Proposed Names

Standard name sensor_band_identifier
Canonical units N/A
Definition Alphanumeric identifier of a sensor band.
Standard name sensor_band_central_wavelength
Canonical units m
Definition The central wavelength of a sensor's band, calculated as the first moment of the band's normalized spectral response function.
Standard name sensor_band_central_wavenumber
Canonical units m-1
Definition The central wavenumber of a sensor's band, calculated as the first moment of the band's normalized spectral response function.
Standard name sensor_band_central_frequency
Canonical units Hz
Definition The central frequency of a sensor's band, calculated as the first moment of the band's normalized spectral response function.
Standard name time_interval
Canonical units s
Definition An interval of time.
Standard name datetime_iso8601
Canonical units N/A
Definition String containing date-time information in one of the ISO 8601 formats. Variables with this standard name cannot serve as coordinate variables.
Standard name sensor_zenith_angle
Canonical units degree
Definition The angle between the line of sight to the sensor and the local zenith; a value of zero is directly overhead.
Standard name platform_look_angle
Canonical units degree
Definition "platform" refers to the vehicle from which observations are made e.g. airplane, ship, or satellite. Platform look angle is the angle between the line of sight from the platform and the direction straight vertically down. Zero look angle means looking directly beneath the platform.
Standard name sensor_look_angle
Canonical units degree
Definition The angle between the line of sight from the sensor and the direction straight vertically down. Zero look angle means looking directly beneath the sensor.
Standard name platform_azimuth_angle
Canonical units degree
Definition "platform" refers to the vehicle from which observations are made e.g. airplane, ship, or satellite. Platform azimuth angle is the horizontal angle between the line of sight from the observation point to the platform and a reference direction at the observation point, which is often due north. The angle is measured clockwise starting from the reference direction.
Standard name sensor_azimuth_angle
Canonical units degree
Definition The horizontal angle between the line of sight from the observation point to the sensor and a reference direction at the observation point, which is often due north. The angle is measured clockwise starting from the reference direction.
Standard name relative_platform_azimuth_angle
Canonical units degree
Definition Difference between two platform_azimuth_angle values.
Standard name relative_sensor_azimuth_angle
Canonical units degree
Definition Difference between two sensor_azimuth_angle values.
Standard name toa_outgoing_spectral_radiance
Canonical units mW m-2 sr-1 (cm-1)-1
Definition "toa" means top of atmosphere; "outgoing" means emitted toward outer space; "spectral" means per unit wavenumber or as a function of wavenumber. Radiance is the radiant power per unit area in a particular direction per unit of solid angle.
Standard name toa_outgoing_spectral_radiance_mean_within_collocation_target
Canonical units mW m-2 sr-1 (cm-1)-1
Definition An average of toa_outgoing_spectral_radiance observations from sensor's adjacent field of views within a collocation target. Collocation target is an area on the Earth's surface at which observations from at least two sensors are collected. Its size is defined by the sensor with the largest field of view footprint.
Standard name toa_outgoing_spectral_radiance_stdev_within_collocation_target
Canonical units mW m-2 sr-1 (cm-1)-1
Definition Standard deviation of toa_outgoing_spectral_radiance observations from sensor's adjacent field of views within a collocation target. Collocation target is an area on the Earth's surface at which observations from at least two sensors are collected. Its size is defined by the sensor with the largest field of view footprint.
Standard name toa_outgoing_spectral_radiance_mean_within_collocation_scene
Canonical units mW m-2 sr-1 (cm-1)-1
Definition An average of toa_outgoing_spectral_radiance observations within a collocation scene. Collocation scene is a grouping of sensor's adjacent field of views (FOVs) centered on a collocation target. Collocation target is an area on the Earth's surface at which observations from at least two sensors are collected. Its size is defined by the sensor with the largest FOV footprint. Collocation scene's size is typically about twice the size of its collocation target.
Standard name toa_outgoing_spectral_radiance_stdev_within_collocation_scene
Canonical units mW m-2 sr-1 (cm-1)-1
Definition Standard deviation of toa_outgoing_spectral_radiance observations within a collocation scene. Collocation scene is a grouping of sensor's adjacent field of views (FOVs) centered on a collocation target. Collocation target is an area on the Earth's surface at which observations from at least two sensors are collected. Its size is defined by the sensor with the largest FOV footprint. Collocation scene's size is typically about twice the size of its collocation target.
Standard name constant_term_of_spectral_radiance_correction_due_to_intercalibration
Canonical units mW m-2 sr-1 (cm-1)-1
Definition Constant term (offset) of the formula for correcting measured spectral radiance. The correction is derived from intercalibration between the monitored and the reference sensor. The resulting corrected spectral radiance of the monitored sensor becomes comparable with measured spectral radiance of the reference sensor. "Spectral" means per unit wavenumber or as a function of wavenumber. Radiance is the radiant power per unit area in a particular direction per unit of solid angle.
Standard name linear_term_of_spectral_radiance_correction_due_to_intercalibration
Canonical units 1
Definition Linear term (slope) of the formula for correcting measured spectral radiance. The correction is derived from intercalibration between the monitored and the reference sensor. The resulting corrected spectral radiance of the monitored sensor becomes comparable to measured spectral radiance of the reference sensor. "Spectral" means per unit wavenumber or as a function of wavenumber. Radiance is the radiant power per unit area in a particular direction per unit of solid angle.
Standard name quadratic_term_of_spectral_radiance_correction_due_to_intercalibration
Canonical units m2 sr cm-1 mW-1
Definition Quadratic term of the formula for correcting measured spectral radiance. The correction is derived from intercalibration between the monitored and the reference sensor. The resulting corrected spectral radiance of the monitored sensor becomes comparable to measured spectral radiance of the reference sensor. "Spectral" means per unit wavenumber or as a function of wavenumber. Radiance is the radiant power per unit area in a particular direction per unit of solid angle.
Standard name covariance_between_constant_and_linear_terms_of_spectral_radiance_correction
Canonical units mW m-2 sr-1 (cm-1)-1
Definition Covariance between constant_term_of_spectral_radiance_correction_due_to_intercalibration and linear_term_of_spectral_radiance_correction_due_to_intercalibration values.
Standard name toa_brightness_temperature_of_standard_scene
Canonical units K
Definition "toa" means top of atmosphere. Brightness temperature of a body is the temperature of a black body which radiates the same power per unit solid angle per unit area at a given wavenumber. Standard scene is a target area with typical Earth surface and atmospheric conditions that is accepted as a reference. The top-of-atmosphere radiance of the standard scene is calculated using a radiative transfer model for a given viewing geometry. The resultant top-of-atmosphere spectral radiance is then integrated with a sensor's spectral response function and converted to equivalent brightness temperature.
Standard name toa_brightness_temperature_bias_at_standard_scene_wrt_intercalibration
Canonical units K
Definition The difference between top-of-atmosphere (TOA) brightness temperature of the reference sensor and TOA brightness temperature of the monitored sensor. This TOA brightness temperature difference is a measure of the calibration difference between the monitored and reference sensors. Standard scene is a target area with typical Earth surface and atmospheric conditions that is accepted as a reference. Brightness temperature of a body is the temperature of a black body which radiates the same power per unit solid angle per unit area at a given wavenumber. TOA brightness temperature of the standard scene is calculated using a radiative transfer simulation for a given viewing geometry. The resultant top-of-atmosphere spectral radiance is then integrated with each sensor's spectral response function and converted to equivalent brightness temperature.

Table Template for Standard Name Proposals

Standard name ...standard name...
Canonical units ...units...
Definition ...text...