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NOTICE: This version of the NSF Unidata web site (archive.unidata.ucar.edu) is no longer being updated.
Current content can be found at unidata.ucar.edu.
To learn about what's going on, see About the Archive Site.
I have been following the CF Profile and CDL and wonder if there has been consideration of several items relating to instrument physics and mathematical representations of that physics. So 1. Has there been a discussion of how to represent Time Series data that has been transformed to Fourier spectra or two or three dimensional fields that use a spherical harmonics representation? It looks like the current conventions consider only data sampled directly in space (usually longitude, latitude, and altitude) and time. Fourier or spherical harmonics expansion coefficients depend on all the temporal or spatial points used to compute them, although the weightings depend on which coefficient is selected for examination. 2. Has there been a discussion as to whether the CF profiles need to consider the interpolating functions between the sampled data points? This concern arises if one wants to compare two collections of data that may have a point sampling, but which might use different functions for interpolating between the samples. There is a deeper concern that follows. One question that arises is whether two data collections should be considered identical if the interpolating functions are different - even if the data values at the sampled points are the same. 3. Has there been a discussion about how to deal with the tradeoff between resolution and uncertainty when such instruments as satellite-borne infrared temperature sounders invert the measurements to retrieve vertical temperature profiles or when airborne or satellite-borne imagers do orthorectification that needs to include the instrument Point Spread Function? 4. Has there been a discussion about what to do with the different altitude axes (geometric altitude, pressure altitude, and sigma coordinates)? If one chooses equal spacing in one of these, then the others are not going to produce equally sampled data points. For example, if we assume that the atmosphere is in hydrostatic equilibrium, then a grid with evenly spaced coordinates in pressure altitude will not have evenly spaced coordinates in geometric altitude if the temperature field has spatial variabilities or such phenomena as inversions. Furthermore, to convert from one coordinate system to another, the algorithms are going to need a vertical temperature profile and perhaps a humidity profile. I assume that these additional fields would need to be added to the data representation in some of the arrays. 5. In representing radiances, does the CF profile intend to treat the direction of propagation as having at least two coordinates (zenith angle and azimuth) as separate dimensions - and perhaps an additional one for solar zenith? 6. Has there been discussion of the correlations and dimensions involved in some of the stratospheric sounding instruments (SAGE, MLS, for example), in which there is a correlation invoked by the scanning geometry? 7. Has there been discussion of how to handle such complex scanning patterns as the MISR stereoscopic camera or the CERES scanning patterns that use directionality of radiances to create stereoscopic movies or sample angular patterns of emitted and reflected radiance? 8. Has there been a discussion as to whether or not vertical "picket fence" sampling by satellite-borne lidars and radars should be handled as "swaths"? I'm aware that NASA's ECS project used that approach in HDF-EOS - but I'm not sure that the patterns of image rows (Landsat or MODIS) have similar characteristics to such samples as Lidar shots. As a note, I'm a retired federal scientist who has led the ERBE and CERES science teams as PI and then moved over into managing the LaRC DAAC. I've taught courses on radiative transfer, including one on remote sensing, which used the weighting functions in inversions for temperature. Bruce R. Barkstrom e-mail: brbarkstrom@xxxxxxxxx cell: (828) 337-7128
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