Dear Alison,
Thank you for the detailed analysis of my proposed standard names and
for summarizing efficiently all outstanding issues. My replies to your
questions are below.
On Thu, Jun 6, 2013 at 9:36 AM, <alison.pamment at stfc.ac.uk> wrote:
> 6) sensor_zenith_angle (degree)
>
> 'sensor_zenith_angle is the angle between the line of sight to the sensor and the local zenith at the observation target; a value of zero is directly overhead the observation target. Local zenith is a line perpendicular to the Earth's surface at a given location. "Observation target" means a location on the Earth defined by the sensor performing the observations. A standard name also exists for platform_zenith_angle, where "platform" refers to the vehicle from which observations are made e.g. aeroplane, ship, or satellite. For some viewing geometries the sensor and the platform cannot be assumed to be close enough to neglect the difference in calculated zenith angle.'
I agree with the definition.
> One further question: do we need to specify in which sense the angle is measured, e.g., 'The angle is measured clockwise starting from directly overhead'?
This angle is measured starting from directly overhead and its range
is from zero (directly overhead) to 180 degrees (directly below).
Perhaps the range can be included?
> 7) platform_look_angle (degree)
>
> ' "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.'
>
> Aleksander and Jonathan have discussed an alternative name of 'platform_view_angle'. Aleksander, are you OK to use that version of the name?
Yes.
> Jonathan has also asked for the sign convention of the angle to be clarified in the definition (similar to my comments above on zenith angle).
There is no standardized sign convention for this angle in satellite
remote sensing so I left that part out from the definition.
> 8) sensor_look_angle (degree)
>
> '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.'
>
> As with (7), do we want to use 'look' or 'view'? What is the sign convention for the angle?
Fine with "view". Same reason as in (7).
> 9) platform_azimuth_angle (degree)
>
> ' "platform" refers to the vehicle from which observations are made e.g. aeroplane, 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 positive, starting from the reference direction. A comment attribute should be added to a data variable with this standard name to specify the reference direction. A standard name also exists for sensor_azimuth_angle. For some viewing geometries the sensor and the platform cannot be assumed to be close enough to neglect the difference in calculated azimuth angle.'
>
> Definition modified to recommend specification of reference direction. This sentence should also be added to the definition of the existing solar_azimuth_angle name. Cross-reference added to sensor_azimuth_angle.
>
> This name is still under discussion, pending agreement on the details of the definition.
I am fine with the reworded definition.
> 10) sensor_azimuth_angle (degree)
>
> 'sensor_azimuth_angle is 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 positive, starting from the reference direction. A comment attribute should be added to a data variable with this standard name to specify the reference direction. A standard name also exists for platform_azimuth_angle, where "platform" refers to the vehicle from which observations are made e.g. aeroplane, ship, or satellite. For some viewing geometries the sensor and the platform cannot be assumed to be close enough to neglect the difference in calculated azimuth angle.'
>
> Definition modified to recommend specification of reference direction. Cross-reference added to platform_azimuth_angle.
>
> This name is still under discussion, pending agreement on the details of the definition.
No objections.
> 11) relative_platform_azimuth_angle (degree)
>
> 'relative_platform_azimuth_angle is the difference between the viewing geometries from two different platforms over the same observation target. It is the difference between the values of two quantities with standard name platform_azimuth_angle. "Observation target" means a location on the Earth defined by the sensor performing the observations. A standard name also exists for relative_sensor_azimuth_angle. For some viewing geometries the sensor and the platform cannot be assumed to be close enough to neglect the difference in calculated azimuth angle.'
>
> Definition expanded to reflect points made in the discussion and for consistency with definitions of other proposed satellite names. Cross-reference to relative_sensor_azimuth_angle added. Jonathan has asked whether there is a sign convention for this name. The convention, or lack of one, should be stated explicitly in the definition.
>
> This name is still under discussion, pending agreement on the details of the definition.
I am not aware of any standard sign convention in use in satellite
remote sensing.
> 12) relative_sensor_azimuth_angle (degree)
>
> ' relative_sensor_azimuth_angle is the difference between the viewing geometries from two different sensors over the same observation target. It is the difference between the values of two quantities with standard name sensor_azimuth_angle. "Observation target" means a location on the Earth defined by the sensor performing the observations. A standard name also exists for relative_platform_azimuth_angle, where "platform" refers to the vehicle from which observations are made e.g. aeroplane, ship, or satellite. For some viewing geometries the sensor and the platform cannot be assumed to be close enough to neglect the difference in calculated azimuth angle.'
>
> Definition expanded to reflect points made in the discussion and for consistency with definitions of other proposed satellite names. Cross-reference to relative_sensor_azimuth_angle added. Jonathan has asked whether there is a sign convention for this name. The convention, or lack of one, should be stated explicitly in the definition.
>
> This name is still under discussion, pending agreement on the details of the definition.
See my reply for 11).
> 13) toa_outgoing_radiance_per_unit_wavenumber (mW m-2 sr-1 (cm-1)-1)
>
> ' "toa" means top of atmosphere. The TOA outgoing radiance is the upwelling radiance, i.e., toward outer space. Radiance is the radiative flux in a particular direction, per unit of solid angle. In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics.'
>
> Definition modified to make wording more consistent with existing 'toa_outgoing' names. OK?
Yes.
> I have a question about the units. I fully accept that you want to use mW m-2 sr-1 (cm-1)-1 in the netCDF files, but for canonical units we usually stick with basic SI units which for this quantity would be W m-2 sr-1 (m-1)-1. Udunits would convert quite happily between the two, and W m-2 is used for existing toa outgoing fluxes, so is it OK to list W m-2 sr-1 (m-1)-1 in the standard name table?
Yes.
> 14) toa_outgoing_radiance_per_unit_wavelength (mW m-2 sr-1 um-1)
>
> ' "toa" means top of atmosphere. The TOA outgoing radiance is the upwelling radiance, i.e., toward outer space. Radiance is the radiative flux in a particular direction, per unit of solid angle. In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics.'
>
> Definition modified to make wording more consistent with existing 'toa_outgoing' names. OK?
Yes.
> As with (13) I have a question about units. Can we use canonical units of W m-2 sr-1 m-1 in the standard name table?
Yes.
> 15) toa_outgoing_radiance_per_unit_wavenumber_mean_within_collocation_target (mW m-2 sr-1 (cm-1)-1)
>
> [...]
>
> Can we use canonical units of W m-2 sr-1 (m-1)-1 in the standard name table?
Yes.
> 16) toa_outgoing_radiance_per_unit_wavenumber_stdev_within_collocation_target (mW m-2 sr-1 (cm-1)-1)
>
> [...]
>
> Can we use canonical units of W m-2 sr-1 (m-1)-1 in the standard name table?
Yes.
> 17) toa_outgoing_radiance_per_unit_wavenumber_mean_within_collocation_scene (mW m-2 sr-1 (cm-1)-1)
>
> [...]
>
> Can we use canonical units of W m-2 sr-1 (m-1)-1 in the standard name table?
Yes.
> 18) toa_outgoing_radiance_per_unit_wavenumber_stdev_within_collocation_scene (mW m-2 sr-1 (cm-1)-1)
>
> [...]
>
> Can we use canonical units of W m-2 sr-1 (m-1)-1 in the standard name table?
Yes.
> 19) constant_term_of_radiance_per_unit_wavenumber_correction_due_to_intercalibration (mW m-2 sr-1 (cm-1)-1)
>
> [...]
>
> Can we use canonical units of W m-2 sr-1 (m-1)-1 in the standard name table?
Yes.
> Discussion between Martin and Aleksander has established that this is a quantity that is generally applicable to remote sensing observations. Martin has asked for the definition of the covariance name (22) to be expanded and I wonder whether we need some more detailed description for this name too. Are there are many 'intercalibration' algorithms and should the data variable be accompanied by a comment attribute to say which algorithm was used, or give a reference to it? Or is there one generally accepted method that we can reference in the definition? It is fine to have quite detailed explanations in the text, for example, some of the sea_surface_wave spectral names have very specific definitions. Do we need something like that for this quantity?
There are many intercalibration algorithms. I am not in favor of
mentioning how to document algorithms in the definition.
> 20) linear_term_of_spectral_radiance_correction_due_to_intercalibration (1)
>
> ' linear_term_of_spectral_radiance_correction_due_to_intercalibration is the 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 radiative flux in a particular direction, per unit of solid angle. In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics.'
>
> My comments for (19) also apply to this proposal.
>
> I note that in http://wiki.esipfed.org/index.php/Standard_Names_For_Satellite_Observations#Proposal_.232 all the other 'spectral' names have been altered to use 'per_unit_wavelength' or 'per_unit_wavenumber' so that correct units can be assigned. Units of '1' for this quantity may mean that in some sense it is less necessary to specify whether the spectrum is given in terms of wavelength, wavenumber, or frequency, but I think for consistency with the other proposed names it would be better to use 'per_unit_wavenumber' for this name too. Also, the definition on the wiki page for the covariance name does refer to linear_term_of_radiance_per_unit_wavenumber_correction_due_to_intercalibration, so perhaps the intention was to modify this name and it got missed accidentally?
Yes, the term "spectral" should have been replaced by "per_unit_wavenumber".
> 21) quadratic_term_of_radiance_per_unit_wavenumber_correction_due_to_intercalibration (mW-1 m2 sr cm-1)
>
> ' quadratic_term_of_radiance_per_unit_wavenumber_correction_due_to_intercalibration is the quadratic term of the formula for correcting measured spectral radiance expressed as a function of wavenumber. 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. Radiance is the radiative flux in a particular direction, per unit of solid angle. In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics.'
>
> My comments for (19) also apply to this proposal.
My reply is the same as for (19).
> 22) covariance_between_constant_and_linear_terms_of_radiance_per_unit_wavenumber_correction_due_to_intercalibration (mW m-2 sr-1 (cm-1)-1)
After reviewing all the comments received so far and overall
discussion of the other proposed standard names it is best to withdraw
this name. It is not generally needed for remote sensing data and
there may be more appropriate ways of describing this and similar
kinds of data in the future.
> 24) toa_brightness_temperature_bias_at_standard_scene_wrt_intercalibration (K)
>
> [...]
>
> Jonathan has suggested a reordering of this name to be bias_in_toa_brightness_temperature_of_standard_scene_wrt_intercalibration and has also asked whether the 'wrt_intercalibration' is really needed. Are other kinds of bias likely to be calculated?
Yes.
> If so then we should keep 'intercalibration' in the name.
Agree.
> Also, shouldn't it be 'due_to' rather than 'wrt' as in the other names?
Agree, so new name would be:
bias_in_toa_brightness_temperature_of_standard_scene_due_to_intercalibration
?
> I am currently preparing the next update of the standard name table. The accepted names in this thread will, of course, be included. If we can resolve the outstanding questions about the names that are close to agreement then many of these could also be accepted and included in the next update.
Thank you again for thorough review.
-Aleksandar
Received on Tue Jun 11 2013 - 12:56:17 BST
