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Note the overlap/duplication of these variables (platform_latitude, platform_longitude, and platform_attitude) with projection parameters. For example, the new geostationary projection (see trac item #72) includes parameters for platform longitude and platform attitude (no need for latitude because by definition platform is at the equator) Not sure how the projections for polar satellite data support geo-location of data points. very respectfully, randy On Feb 19, 2013, at 1:35 PM, Jim Biard wrote: > A few comments/questions regarding the platform latitude, longitude, and > altitude: > > Sub-satellite point means the intersection of a line from the center of the > Earth to the satellite with the surface of the Earth. > > Is referring to the sub-satellite point necessary? At first glance, I think > it isn't needed. > > I don't see a need to make any of these names satellite-specific. > > Use the word height instead of altitude in the definition for > platform_altitude to avoid recursion (the altitude is the altitude). > > Latitude, longitude, and altitude should be considered in relation to the > coordinate system defined for the file. I think it would be best to remove > the reference to mean sea level from the definition of the altitude. It is > the height above the coordinate system vertical datum, which might not be sea > level. (In particular, if geometric heights on an ellipsoid are used, there > can be significant differences. And, in fact, WGS84 and the WGS84 ellipsoid > are often used in satellite work.) > > And while I'm at it, would it also be useful to include platform_x, > platform_y, and platform_z in the set? These would be useful in the case > where the coordinates are in Earth-centered Cartesian coordinates (ECF, ECI), > as well as cases where a projected coordinate system was used. The projected > coordinate case would clearly be for a subset of an orbit, but could still be > completely valid. This would also be useful for other moving platform cases > (aircraft, ships, etc). > > Grace and peace, > > Jim > > Jim Biard > Research Scholar > Cooperative Institute for Climate and Satellites > Remote Sensing and Applications Division > National Climatic Data Center > 151 Patton Ave, Asheville, NC 28801-5001 > > jim.biard@xxxxxxxx > 828-271-4900 > > On Feb 19, 2013, at 12:47 PM, Mike Grant <mggr@xxxxxxxxx> wrote: > >> On 19/02/13 15:00, Mike Grant wrote: >>> To make replies easier and as some of us (normally me!) may be too lazy >> >> And now for a reply (comments inline).. >> >> First, did you coordinate with Aleksandar Jelenak's proposed new names? >> They should be in the list archive for this list 19/Sept/2012 "New Standard >> Names for Satellite Data" and for the main CF-metadata list on 7/Oct/2012 >> "New standard names for satellite obs data" and summarised at >> http://wiki.esipfed.org/index.php?title=Standard_Names_For_Satellite_Observations, >> before it got derailed by string-based time variables debate. >> >> I think the platform ones fit well with your proposals (so perhaps you >> already coordinated?) - perhaps by reincluding or referencing them in your >> submission, you could rescue those parts from the time-string swamp. >> >> Either way, it may be wise to split these proposals into multiple parts to >> ensure that the whole set aren't hung up on a single argument. Perhaps split >> into 3 parts by platform, sensor and toa names? >> >>> azimuth_angle >>> * degrees >>> * Azimuth angle is the angle measured towards the east, from north, >>> along the astronomical horizon to the intersection of the great circle >>> passing through the point and the astronomical zenith with the >>> astronomical horizon. >>> >>> platform_latitude >>> * degrees_north >>> * Latitude of the satellite measured at the sub-satellite point >>> >>> platform_longitude >>> * degrees_east >>> * Longitude of the satellite measured at the sub-satellite point >>> >>> platform_altitude >>> * m >>> * Altitude of the satellite above mean sea level >> >> If these are specifically about satellites, it may be worth renaming them to >> satellite_XXX. I think it would be more useful to keep them as platforms, >> in which case perhaps change the word "satellite" to "platform" in the >> descriptions. >> >> Either way, it would be nice to more clearly define what's meant by the >> "sub-satellite point" for non-specialists (CF is used by all sorts of >> people) or, better, rephrase it in generic "platform" language. Is this the >> position on the surface/geoid/ellipsoid (intersection of the line between >> the platform location and the centre of the Earth with the geoid/ellipsoid)? >> >> It might be worth stealing parts of the definition of the general term >> "altitude" as it's nicely written: >> "Altitude is the (geometric) height above the geoid, which is the reference >> geopotential surface. The geoid is similar to mean sea level." >> >>> sensor_band_spectral_width >>> * cm-1 >>> * Bandwidth of the satellite’s spectral channel >> >> This also fits nicely with the sensor_band_ proposals Aleksandar made on >> this list, but they didn't seem to go onto the CF list. Might be worth >> rescuing too, unless Aleksander is reading and had another reason not to >> submit? >> >> Again, it would be good to replace "satellite" with "sensor". Unless it's >> intentionally vague, perhaps define more clearly what's meant by the >> bandwidth (e.g. full width half max?) >> >>> toa_spectral_irradiance >>> * mW m-2 (cm-1)-1 >>> * "toa" means top of atmosphere; irradiance which is relevant for any >>> sensor measuring in the UV-VIS and NIR. This parameter is reported by >>> integrating over the whole sphere. >> >> Might be worth stealing wording from other standard definitions >> incorporating irradiance, e.g. >> >> omnidirectional_spectral_spherical_irradiance_in_sea_water >> - "spectral" means per unit wavelength or as a function of wavelength; >> spectral quantities are sometimes called "monochromatic". Radiation >> wavelength has standard name radiation_wavelength. Omnidirectional spherical >> irradiance is the radiation incident on unit area of a spherical (or "4-pi") >> collector. It is sometimes called "scalar irradiance". Radiation incident on >> a 2-pi collector has standard names of "spherical irradiance" which specify >> up/downwelling. >> >> In fact, perhaps the name should be >> toa_omnidirectional_spectral_spherical_irradiance ? >> >>> toa_spectral_reflectance >>> * 1 (dimensionless) >>> * Ratio of radiance to irradiance I/I0, reflection from a thick layer >>> where the layer, here the atmosphere, is part of the reflection's property. >> >> Stealing a few bits from toa_bidirectional_reflectance, perhaps.. >> >> Reflectance is the ratio of the energy of the reflected to the incident >> radiation. "spectral" means per unit wavelength or as a function of >> wavelength; spectral quantities are sometimes called "monochromatic". A >> coordinate variable of radiation_wavelength or radiation_frequency can be >> used to specify the wavelength or frequency, respectively, of the radiation. >> "toa" means top of atmosphere. toa_spectral_reflectance is the ratio of >> radiance to irradiance I/I0, reflection from a thick layer where the layer, >> here the atmosphere, is part of the reflection's property. >> >>> toa_outgoing_inband_radiance >>> * mW m-2 sr-1 >>> * "toa" means top of atmosphere; "outgoing" means emitted toward outer >>> space; the radiance is integrated over a discrete band. >> >> I think this one is quite new to CF (integrating over a band), so you're >> probably setting a standard here. It may be worth saying that the band can >> be specified by (e.g.) a coordinate variable or other ancillary data. >> >>> toa_reflectance >>> * Percent >>> * Ratio of the energy of reflected to incident light at the top of >>> atmosphere. >> >> Steal most of the text from toa_bidirectional_reflectance? >> >> Should this be unitless, like toa_bidirectional_reflectance and >> toa_spectral_reflectance? >> >> Ok, that was longer than I thought - hope it was helpful, but feel free to >> take what you wish and reject what you don't. I think the splitting idea >> may be worth it to avoid getting tied up in arguments though. >> >> Cheers, >> >> Mike. >> >> >> Latest news: www.pml.ac.uk and @PlymouthMarine >> >> Plymouth Marine Laboratory (PML) is a company limited by guarantee >> registered in England & Wales, company number 4178503. Registered Charity >> No. 1091222. Registered Office: Prospect Place, The Hoe, Plymouth PL1 3DH, >> UK. >> This message is private and confidential. If you have received this message >> in error, please notify the sender and remove it from your system. You are >> reminded that e-mail communications are not secure and may contain viruses; >> PML accepts no liability for any loss or damage which may be caused by >> viruses. >> >> _______________________________________________ >> cf-satellite mailing list >> cf-satellite@xxxxxxxxxxxxxxxx >> For list information or to unsubscribe, visit: >> http://www.unidata.ucar.edu/mailing_lists/ > > _______________________________________________ > cf-satellite mailing list > cf-satellite@xxxxxxxxxxxxxxxx > For list information or to unsubscribe, visit: > http://www.unidata.ucar.edu/mailing_lists/ ____________________________________ Randy C. Horne (rhorne@xxxxxxxxxxxxxxxxx) Principal Engineer, Excalibur Laboratories Inc. voice & fax: (321) 952.5100 url: http://www.excaliburlabs.com
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