PATMOS-x AVHRR Pathfinder Atmospheres - Extended

Analysis Tools

See also: Data

On this page, you will find some tools to allow you to read, display and analyze the PATMOS-x gridded data.

NOTE: Data on ftp site is compressed with gzip. Uncompress before using these tools.

Reading PATMOS-x data in IDL

An IDL program, read_clavrx_hdf.pro, has been written by Michael Pavolonis of UW/CIMSS to view the CLAVR-x/PATMOS-x HDF files. This routine, documented in the top of the IDL source code, has optional arguments to return many attributes of each parameter.

Here are some examples using a file named clavrx_n17_des_05_1_2004_197.cell.hdf

  • To read in the total cloud fraction (sds name = 'frac_total_cld') do this: cloud_fraction = read_clavrx_hdf('clavrx_n17_des_05_0_2004_197.cell.hdf', 'frac_total_cld')
  • To read in the mean channel 4 radiance for clear pixels (sds name = ch4_clr) to the following ch4_rad_clr = read_clavrx_hdf('clavrx_n17_des_05_0_2004_197.cell.hdf', 'ch4_clr')
  • To read in the mean channel 4 radiance for clear pixels (sds name = ch4_clr) to the following ch4_rad_clr = read_clavrx_hdf('clavrx_n17_des_05_0_2004_197.cell.hdf', 'ch4_clr')
  • To read in the mean channel 4 radiance converted to a brightness temperature, do this
    ch4_bt_clr = read_clavrx_hdf('clavrx_n17_des_05_0_2004_197.cell.hdf', 'ch4_clr',/temperature)

    note, the /temperature keyword does not convert the radiance standard deviation to brightness temperature standard deviations.
  • To read in the LST standard deviation (sds = lst_clr_std) and some of its attributes, do this
    lst = read_clavrx_hdf('clavrx_n17_des_05_0_2004_197.cell.hdf', 'lst_clr_std',units=units, day=start_day)

    where units will have the value of unit of this parameter (K) and day will have the value of the Julian day of this data (197).

Displaying PATMOS-x data in IDL

The idl program map_clavrx.pro uses read_clavrx_hdf.pro to produce global images from any gridded file. This can run as follows within idl (using the same example)
map_clavrx, 'clavrx_n18_des_05_0_2005_217.cell.hdf', 'cld_opd_ir_ice', max = 4.0
produces the following image of cld_opd_ir_ice (cloud optical depth of ice cloud from ir method)

sample image

The following arguments are optional to map_clavrx.pro

  • /subflg keyword - allows a subset of the globe to be imaged at a higher resolution
  • /jpg keyword - creates a jpeg image
  • min - the minimum value to plot (zero ignored)
  • max - the maximum value to plot

In addition, you will need to have cbar.pro and saveimage.pro (written by Liam Gumley) in place that IDL will look for them.  Note, map_clavrx.pro requires compilation before running. (.rnew map_clavrx).

Viewing a Time-Series from PATMOS-x Data

The IDL code, clavrx_time_series.pro, allows for a time-series of any PATMOS-x variable to be displayed or saved to an ascii file over any region. This program uses read_clavrx_hdf.pro. To make a time series, the first step is to construct a file called "time_series_input" that contains a list of the data-sets to be included in the time series. The data-sets can be daily and/or monthly. The following examples show some of the functionality of this program.

  • sample time_series_input  file
    Note that the annonation included on some lines are used to label the plots.

    /data4/patmosx/1995/daily/clavrx_n14_des_05_0_1995_182.cell.hdf  182
    /data4/patmosx/1995/daily/clavrx_n14_des_05_0_1995_183.cell.hdf 
    /data4/patmosx/1995/daily/clavrx_n14_des_05_0_1995_184.cell.hdf  
    /data4/patmosx/1995/daily/clavrx_n14_des_05_0_1995_185.cell.hdf 
    /data4/patmosx/1995/daily/clavrx_n14_des_05_0_1995_186.cell.hdf 
    /data4/patmosx/1995/daily/clavrx_n14_des_05_0_1995_187.cell.hdf 
    /data4/patmosx/1995/daily/clavrx_n14_des_05_0_1995_188.cell.hdf 
    /data4/patmosx/1995/daily/clavrx_n14_des_05_0_1995_189.cell.hdf 
    /data4/patmosx/1995/daily/clavrx_n14_des_05_0_1995_190.cell.hdf  190
  • Example use for a time series of one variable over user-defined area
    clavrx_time_series, 'ndvi_clr_sfc', 15,  range=[0.2,0.7], /area this produces the following image when an area over the USA is selected.

    ndvi time series
  • Example of a time-series for one grid-cell.
    This command uses the same data to make a time series of the same parameter over a cell near Lubbock, Texas.

    clavrx_time_series, 'ndvi_clr_sfc', 15, geol=[33.7, -101.8], range=[0.2,0.7]

    the following image is produced.
    lubbock ndvi

Reading PATMOS-x data in MATLAB

Aleksandar Jelenak has coded a MATLAB routine with similar functionality to read_clavrx_hdf.pro called read_clavrx_hdf.m.