Does NSIDC have tools to extract and geolocate polar stereographic data?

NSIDC provides software tools to extract and geolocate data in a polar stereographic projection derived from passive microwave instruments, as well as masking tools that limit the influence of weather effects on sea ice concentrations. All tools are available by FTP. The tools work with the polar stereographic gridded passive microwave data sets at NSIDC.

Types of tools include:

1. Data extraction tools
2. Geocoordinate tools
3. Masks & overlays

Data extraction tools

The following data extraction tools allow you to extract and read the data from the data files.

extract.pro

An IDL program that allows you to open a brightness temperature grid file and read it into an array, making it available for further manipulation in IDL or to write to hard disc. After the program has read the user-indicated time range, an array is returned with a 2-byte integer array of brightness temperatures expressed in tenths of a kelvin (0.1 K). For example, a value of 2358 translates to 235.8 K.

Access: FTP

Applicable data sets

• Nimbus-5 ESMR Polar Gridded Brightness Temperatures

IDL Routines for Passive Microwave Data: Usage Example - extract.pro

Items in bold indicate user input. 

IDL> extract,array

% Compiled module: EXTRACT.Enter the processing type(1 = near-real-time)(2 = polar grids from hard drive)

: 1

Enter start and end dates for animation (yyyymmdd, e.g., 19950610).

Start Date: 20010404End Date: 20010404

Enter the channel to be extracted1 2 3 4 5 6 7--- --- --- --- --- --- ---19V 19H 22V 37V 37H 85V 85HEnter position of parameter (1-7)

: 2

Enter the hemisphere(1 = northern)(2 = southern)

: 1

Enter the full name of the directory that the Tb files are in.(Note: must correctly use upper and lower case letters.)

: /usr2/projects/tb_tools/usr2/projects/tb_tools/NRTSI_SSMIF13_20010404_N.19H

% Loaded DLM: HDF.

IDL> 

extract_

extract_ice.pro

An IDL program that extracts a time series of polar sea ice data. The extraction routine works on both the daily and monthly sea ice files allowing users to select and display sea ice concentrations. For monthly data, users may select which image threshold to view (0, 5, 10, or 15% ice cut off).

Applicable data sets

• Nimbus-5 ESMR Polar Gridded Sea Ice Concentrations

Access: FTP

IDL routines for passive microwave data: Usage example - extract_ice.pro

Items in bold indicate user input. 

IDL> extract_ice,array

% Compiled module: EXTRACT_ICE.Enter the processing type (1 = near-real-time)(2 = polar grids)

: 1

Enter start and end dates (yyyymmdd, e.g., 19950610).

Start Date: 20010404End Date: 20010404

Enter the hemisphere (1 = northern)(2 = southern)

: 1

Enter the full name of the directory that the sea ice files are in.(Note: must correctly use upper and lower case letters.)

: /usr2/projects/tb_tools

Enter the satellite number (e.g., 8, 11, or 13)

: 13

/usr2/projects/tb_tools/NRTSI_SSMIF13_20010404_N.BIN/usr2/projects/tb_tools/NRTSI_SSMIF13_20010404_N.BIN

IDL> 

Geocoordinate tools

For data set users who need the latitude and longitude of the center of any cell in the grid, the following geocoordinate tools are available.

Land masks

NSIDC provides masks and overlays to supply users with many options for concealing unwanted regions or overlaying coastlines and latitude/longitude grids. The land masks are useful for concealing the land of the Northern and Southern Hemispheres prior to processing of the data. The files are divided into two categories: Northern Hemisphere and Southern Hemisphere.

Beginning with the SMMR era, the first masks NSIDC developed were landmask.ntb and landmask.stb. Other masks were later added for use with SSM/I F8 data. The last set of masks to be added to the series are those beginning with gsfc, which were originally developed for use with SSM/I F11 and F13. However, all of the masks provided here will work across all platforms (SMMR and SSM/I).

The relatively slight differences in numbers of SSM/I-grid pixels masked as land can introduce discrepancies in analyses of time series spanning the SMMR and SSM/I period. One method of addressing this issue is to generate a composite mask in which all pixels mapped as land in any of the masks are coded as land pixels in the composite mask. Use of such a composite mask improves the consistency of the SMMR and SSM/I record at the expense of masking additional ocean areas as land. A composite of the CIA World Data Bank I and II (GSFC-1 and JPL-1) has been produced by J. Maslanik at NSIDC.

Another issue is the effect of contamination of coastal ocean pixels by their proximity to land. Such proximity can modify the brightness temperatures of coastal ocean pixels, producing false ice concentration values along some coasts. These pixel mixing errors are considered in the summer 1996 issue of NSIDC Notes (Issue no. 18). Maslanik et al. (1996) discuss the effects of such land contamination in introducing differences between SMMR and SSM/I time series, and they describe the use of a modified land mask where land areas are extended to mask substantial contamination. 

Land overlays

The land overlays are useful for overlaying coast line and latitude/longitude grids on top of images and processed data. The files are broken down into two categories: Northern Hemisphere and Southern Hemisphere.

Missing data mask

The circular section over the Northern Hemisphere pole (known as the pole hole) is never measured due to orbit inclination. The following mask is available for the pole hole region not covered by the SMMR and SSM/I instruments.
 

Region masks

The region masks are smaller areas than the land masks although they can be used as land masks using the pixel value of 11.