17-May-2012

EO Data Access
		How to Apply

		How to Access

Services

Site Map

Frequently asked questions

Glossary

Credits

Search
Advanced Search

BEST Examples

Tutorial: Quick Look Generation and Image Extraction using BEST for Windows OS

In this simple example a Quick Look image is generated from an ASAR Image Mode Precision Image product. From the quick look image it is possible to define a region of interest. The Image Extraction tool is then used to select this region and read it into the BEST software. Finally a further quick look is made of the extracted region.

Example Data

It is possible to download example sets of ASAR data from the Envisat User Services webpages. Go to this link:

http://envisat.esa.int/services/sample_products/asar/DS1/IM/

For this example an Image Mode Precision Image will be used. Download the following ZIP compressed image file into a convenient “working directory”.

ASA_IMP_1PXPDE20020730_095910_000000162008_00108_02166_0020.N1.gz

For this example, a “working directory” called IMP_quick_look has been created:

C:\Best_example\IMP_quick_look

Use the WinZip tool (or something similar) to decompress the compressed (.gz) image file into the working directory.

The data was acquired on 30/07/2002 over Flevoland in the Netherlands. The acquisition started at the time 09 hours, 59 minutes and 10 seconds UTC and is a part of Envisat orbit 2166.

Using bestW

Working on a PC running Windows OS, it is easiest to use the BEST software with the “bestW” Visual Basic interface*. To activate this, click on the bestW icon in the BESTv421\bin directory (if a bestW icon has already been created, it can be activated directly from the desktop).

* The look of the Visual Basic interface of BEST 4.2.1 is a bit different from that reported in this example but the functions are the same.

Set Up Working Directory

Although it is not necessary, it may be convenient to use the bestW interface to define the directory that will be used to store processed data and parameter files.

To do this use the “Setup Working Directory” option from the Help menu:

Then select a suitable working directory (and click OK), e.g.

Henceforth the bestW dialogue boxes will automatically default to this directory.

Header Analysis

Nearly always the first thing that needs to done with BEST is to perform the Header Analysis function. This decodes the header parameters from a product, which are then used by many of the following Toolbox operations.

Select the Header Analysis tool from the Data Import and Quick Look menu:

For the data used in this example, it will be necessary to select the following options:

When the Header Analysis function has finished there should be three new files in the specified output directory.

1. header_IMP.txt (Full product header information in text format.)

2. header_IMP.HAN (Full product header information in BEST internal format, for use by the software in other tools.)

3. header_analysis_parameters.ini (The “Configurations Settings” file generated by the bestW tool, containing all the parameter information needed to run the BEST software.)

Why these Parameters?

It is instructive to examine the parameters selected above.

Input Media Path : This is the path to the directory where the data is stored. Often data will be located on a CD ROM, therefore often this path will lead to the CD-ROM drive.

Input Product Image : The data product to be used.

Input Media Type : The type of media where the data is currently located. In this example the data is stored on the system hard disk, because it has been downloaded by FTP. However, more commonly it will be on a CD ROM.

Sensor Id : In this instance Envisat ASAR. BEST can also be used with SAR data from ERS-1 and ERS-2. The Sensor ID should be selected before the Input Product Image can be selected.

Sensor Mode : In this instance an Image Mode Product.

Alternating Polarization Dataset : This should be ignored for data that is not in the Alternating Polarisation Mode.

Product Type : For each sensor mode, the product can come at a number of different processed levels. In this instance “PRI” indicates that this is a Level 1b Precision Image.

Data Format : The acronym “MPHSPH” indicates that this data is in the Envisat format.

Source Id : This refers to the “location” format according to where the data has been processed. All Envisat data is processed to exactly the same “MPHSPH” format and this is indicated by the “ESRIN” parameter. For ERS-1 and ERS-2 data the format is slightly different depending on the station at which the data has been processed.

Number Of Volumes : This will nearly always be 1. This refers to the number of files that the data is split into. In exceptional circumstances very large data sets may be split onto several CD ROMs or Exabyte tapes.

Output Dir : This is the path to the directory where the output products will be written.

Annotation File : The name of the product header information in text format, i.e. for examination by the user.

Header Analysis File : The name of the product header information in BEST internal format, for importing into other functions.

Dismount Volume : This determines whether the product, e.g. a CD ROM should be dismounted.

How the BEST Interface Works

When the OK button on the panel (as shown above) is clicked, a MS-DOS Window will pop up and the Header Analysis function will automatically begin. The steps underlying this apparently automated mechanism are that; first, a file is created, in this instance called:

header_analysis_parameters.ini

This file contains all the parameters needed by BEST in order to perform the required operation.

Second, the file is run from a MS-DOS Window.

The BEST software can be run without the bestW tool by creating “header_analysis_parameters.ini” using a standard text editing tool and then executing this file from a MS-DOS window with the command:

best header_analysis_parameters.ini

Quick Look Generation

It is very often useful to produce a "quick look" image of the data. This makes it possible to check that the data covers the intended scene and if necessary, it can help in selecting an area of interest to extract and work on.

The Quick Look function can be performed when the data is still on a CD ROM or Exabyte tape, as well as when it is already on the hard disk.

Select the Quick Look Generation tool from the Data Import and Quick Look menu:

There are 3 output files from this function:

1. IMP_main-quick-look.tif (The Quick Look Tiff image of the image product.)

2. IMP_main-quick-look_grid.tif (Shown below. The Quick Look Tiff image of the image product, with the grid lines as specified in the bestW panel.)

3. IMP_main-quick-look_parameters.ini (The “Configurations Settings” file generated by the bestW tool, containing all the parameter information needed to run the BEST software.)

IMP_main-quick-look_grid.tif (saved here as a jpeg file)

Note: it is not possible to open the TIFF files generated by BEST with all image viewing software. For PC platforms problems should not be encountered using Adobe ® Photoshop ®, Jasc ® Paint Shop Pro™ or Microsoft ® Paint (a standard component of Microsoft Windows found in the Start Menu under Programs > Accessories > Paint).

Full Resolution Extraction

Using the row and column grid on the quick look image created and shown above, a portion of the image is identified that will be read into the internal BEST format.

Select the Full Resolution Extraction tool from the Data Import and Quick Look menu:

In this example only a portion of the total image is selected and extracted. When the “Y” radio button is selected under AOI spec, a further dialogue box pops up, enabling an area of interest to be selected in up to 9 different ways.

There are two outputs from this function.

1. IMP_full-resolution.XTs (The portion of the original image, now stored in the BEST internal format. See the BEST User Manual for a full description of the meaning of the file extension “XTs”.)

2. full-resolution-import.ini (The “Configurations Settings” file generated by the bestW tool, containing all the parameter information needed to run the BEST software.)

Quick Look Generation

In order to examine the new cropped image “IMP_full-resolution.XTs” it can be quickly output to a TIFF file using the Quick Look Generation tool.

This time, when the Quick Look Generation panel is activated; the “File” Input Media Type is selected, to signify that the required image is now in the BEST internal format. When this option is used, the section of the panel requesting the Header Analysis file disappears. This is because data in the BEST internal format contains the header information as well as other information concerning any previous BEST operations.

There are 3 outputs from this function.

1.quick_look_crop.tif (The Quick Look Tiff image of the image product.)

2. quick_look_crop_grid.tif (Shown below. The Quick Look Tiff image of the image product, with the grid lines as specified in the bestW panel. Here the Latitude and Longitude option (LatLon) for the grid type has been selected.)

3. quick_look_crop_parameters.ini (The “Configurations Settings” file generated by the bestW tool, containing all the parameter information needed to run the BEST software.)

quick_look_crop_grid.tif (saved here as a jpeg file)

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry