Re: Regridding and Plotting Satellite Data

Thanks for the quick response,

  Plotting the raw data values hasn't been a problem; the lat2d/lon2d
worked perfectly for that.

  As for the gridding, I've attached a copy of the printVarSummary for
aodr. It does contain the _FillValue attribute straight from the file,
but it is -9999. Should that be -99 since the variable is of type
'short'? Does cssgrid have problems with short?

  Also pertaining to the variable type, the poisson function wanted a
float or double variable.

Walter

printVarSummary(aodr) [raw data]
**************************************************************************
Variable: aodr
Type: short
Total Size: 54810 bytes
            27405 values
Number of Dimensions: 2
Dimensions and sizes: [Cell_Along_Swath_mod04 | 203] x
[Cell_Across_Swath_mod04 | 135]
Coordinates:
Number Of Attributes: 11
  _FillValue : -9999
  valid_range : ( -100, 5000 )
  long_name : AOT at 0.55 micron for both ocean (best) and land
(corrected) with best quality data(Quality flag=3)
  units : None
  scale_factor : 0.001000000047497451
  add_offset : 0
  Parameter_Type : Output
  Cell_Along_Swath_Sampling : ( 5, 2025, 10 )
  Cell_Across_Swath_Sampling : ( 5, 1345, 10 )
  Geolocation_Pointer : Internal geolocation arrays
  hdf_name : Optical_Depth_Land_And_Ocean
************************************************************************
On Sat, 2008-04-19 at 08:24 -0600, Dennis Shea wrote:
> Hello
>
> [1]
> The following is one example of directly plotting 'swath' data
> http://www.ncl.ucar.edu/Applications/eosdis.shtml
> See Examples 4 and 5
>
> [2]
> NCL has two reserved attribute names "lat2d" and "lon2d".
> These are used when the data are 'curvilinear'. Basically,
> whenever the data have 2D lat/lon arrays, the variable being
> plotted should have the lat2d/lon2d arrays associated with it
>
> lat2 = f->Latitude
> lon2 = f->Longitude
> aodr_at_lat2d = lat2 ; associate [assign] the 2d lat/lon
> aodr_at_lon2d = lon2 ; to the variable to be plotted
>
> [3]
> The cssgrid is supposed to ignore missing values [_FillValue].
> Since this is a NASA generated hdf file, I'd be surprised
> if they automatically created the _FillValue attribute. Typically,
> NASA/HDF are blissfully ignorant of *netCDF* conventions.
> WHat does the 'printVarSummary' say. Is there an _FillValue
> attribute? If not, you can manually assign
> aodr@_FillValue = -9999
>
> [4]
> Just for 'fun' try
> poisson_grid_fill( aodr, False, 1, 1500, 1e-2, 0.6, 0)
>
> plot the aodr in the swath region
>
> Good luck
>
> Walter R Sessions wrote:
> > Hello,
> >
> > I'm attempting to regrid MODIS satellite data for a correlation study
> > and have been having difficulty getting it worked out.
> >
> > Since it is satellite data and there will be missing values, I followed
> > the regridding flow chart and have been trying to use the cssgrid
> > function. However, I've been running into the following problems.
> >
> > First, unless I drop the _FillValues, it appears to interpolate to them
> > (in this case, -9999). The values of the contoured scalar are wholly
> > positive, however the contour of the cssgrid derived plot is goes down
> > to the -7e+06 and up into the positive millions.
> >
> > Second, I've been attempting to just plot a section of a swath in the
> > North Pacific, which is all this file contains. The points where it
> > does put data appear to be stretching from the appropriate area, south
> > of Alaska, down past the equator.
> >
> > I've attached the script for reference.
> >
> > It occurs to me that it might be better to attempt to just use an
> > average for the value within a defined grid spacing, but I've been
> > having difficulty in finding how to do that within NCL.
> >
> > Advice on either how to average into a grid or to work with cssgrid is
> > appreciated.
> >
> > Walter
> >
> >
> > I've attempted several variations of resources on and off and still
> > can't get anything that looks accurate.
> >
> > ;*************************************************
> > ; plot_AOD.ncl
> > ;************************************************
> > load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_code.ncl"
> > load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_csm.ncl"
> > load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/contributed.ncl"
> >
> >
> > begin
> > ;-open file and create pointer
> > a =
> > addfile("./MYD04_L2.A2008031.2300.005.2008033054757.pscs_000500293068.hdf","r")
> >
> > ;
> > ;-input array od data (203x135ish)
> > aodr = a->Optical_Depth_Land_And_Ocean
> > printVarSummary(aodr)
> >
> > ;
> > ;-get array of lat/lon coordinates
> > latr = a->Latitude
> > lonr = a->Longitude
> >
> > ;
> > ;-put them both in 1D arrays
> > aod1= ndtooned(aodr)
> > lat1= ndtooned(latr)
> > lon1= ndtooned(lonr)
> > print("LAT_MAX: "+dim_max(lat1))
> > print("LAT_MIN: "+dim_min(lat1))
> > print("LON_MAX: "+dim_max(lon1))
> > print("LON_MIN: "+dim_min(lon1))
> > print("AOD_MAX: "+dim_max(aod1))
> > print("AOD_MIN: "+dim_min(aod1))
> >
> > ;
> > ;-just testing set - should always have missing data
> > if(any(ismissing(aod1))) then
> > print("MISSING AOD DATA")
> > else
> > print("No missing data")
> > end if
> >
> > ;
> > ;-generate output grid (half degree global)
> > ; plon = fspan(-180,180,361)
> > ; plat = fspan(-90,90,181)
> > plon = fspan(-180,180,181)
> > plat = fspan(-90,90,91)
> > plon_at_units = "degrees east"
> > plat_at_units = "degrees north"
> > ;
> > ;-future filtering placeholder
> > aod_filter = aod1
> >
> > ;
> > ;-grid data onto platxplon
> > print("AOD_ONE_DIM : "+dim_max(aod1))
> > aod_grid = cssgrid(lat1,lon1,aod_filter,plat,plon)
> >
> > ; aod_grid!0 = "lat"
> > ; aod_grid!1 = "lon"
> > ; aod_grid&lat = plat
> > ; aod_grid&lon = plon
> >
> > ;-keep for reference
> > ; aod_filter!0 = "lat"
> > ; aod_filter!1 = "lon"
> > ; aod_filter&lat= plat
> > ; aod_filter&lon= plon
> > ; aod_filter&lon_at_units = "degrees east"
> > ; aod_filter&lat_at_units = "degrees north"
> >
> > aod_grid!0 = "lat"
> > aod_grid!1 = "lon"
> > aod_grid&lat = plat
> > aod_grid&lon = plon
> > aod_grid&lon_at_units = "degrees east"
> > aod_grid&lat_at_units = "degrees north"
> >
> > ;
> > ;-create workstation and define colormap
> > wks = gsn_open_wks("x11" ,"ce")
> > ;-gsn_define_colormap(wks,"WhBlGrYeRe")
> > gsn_define_colormap(wks,"testcmap")
> >
> > ;
> > ;-Turn on plotting options then set them
> > res = True ; plot mods desired
> >
> > res_at_cnFillOn = True ; turn on color fill
> > ;-res_at_cnFillMode = "RasterFill" ; rasterize plot
> > res_at_cnLinesOn = False ; turn of contour lines
> > ;-res_at_cnLevelSpacingF = 0.5 ; contour spacing
> > res_at_gsnSpreadColors = True ; use full range of color map
> > res_at_lbLabelStride = 4
> > ;-res_at_pmTickMarkDisplayMode = "Always"; use NCL default lat/lon labels
> > ;
> > res_at_gsnAddCyclic = False
> > res_at_mpMinLatF = -90 ; range to zoom in on
> > res_at_mpMaxLatF = 90.
> > res_at_mpMinLonF = -180.
> > res_at_mpMaxLonF = 180.
> >
> > ;
> > ;-1d monotonic arrays that represent the x/y axes
> > ; res_at_sfXArray = plon
> > ; res_at_sfYArray = plat
> >
> > ;-plot = gsn_csm_contour_map(wks,aod_grid, res)
> > plot = gsn_csm_contour_map_ce(wks,aod_grid, res)
> > end
> >
> > 113,1 Bot
> >
> >
> >
> > _______________________________________________
> > ncl-talk mailing list
> > ncl-talk_at_ucar.edu
> > http://mailman.ucar.edu/mailman/listinfo/ncl-talk
> >
>
>

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Received on Sat Apr 19 2008 - 08:26:54 MDT