Regridding and Plotting Satellite Data

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

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Received on Fri Apr 18 2008 - 17:55:46 MDT