Contents

Introduction

This short document is intended to get a new user familiar with selecting downloading and viewing CaSSIS data. It is intended to be a living document so any feedback or ideas on how to improve it will be useful.

Archive Contents

There are three types of CaSSIS files currently in the archive:

  • Raw files - containing Raw values in 2D arrays
  • Calibrated files - containing radiometrically calibrated values in 2D arrays
  • Stitched files - essentially images just for browse purposes of stitched calibrated data

CaSSIS Filenames

Raw and Calibrated files are named like:

  • cas_raw_sc_20170305t234101-20170305t234105-50-16-ex1-102171730-32-5

Here:

  • raw = processing level, in PDS4 this is raw, partially_processed, calibrated and derived
  • sc = science (hk=housekeeping)
  • 20170305t234101-20170305t234105 = framelet start and end time
  • 50 = Orbit Number
  • 16 = Observation Number within an orbit
  • ex1 = Filter
  • 102171730 = CaSSIS Unique Image Identifier (UID)
  • 32 = Frame Count
  • 5 = Framelet sequence count

Note the main CaSSIS filters are "BLU", "RED", "NIR" and "PAN" (PAN=Panchromatic), some observations will have "MULTI" These observations are for calibration purposes only and represent when the entire array instead of single filter subframes were downlinked. A few observations will also have either "EX1" or "EX2", these use an extended part of the array and are also observations made for calibration purposes.

Stitched files are named like:

  • cas_cal_sc_20200120t022402-20200120t022419-pan-556587978-sti

Archive Contents

There are three types of CaSSIS files currently in the archive:

  • Raw files - containing Raw values in 2D arrays
  • Calibrated files - containing radiometrically calibrated values in 2D arrays
  • Stitched files - essentially images just for browse purposes of stitched calibrated data

How To Navigate the PSA and Isolate an Observation

The Filter

The easiest way to get started is to go to psa.esa.int and in the welcome/home screen start typing CaSSIS and select "CaSSIS Instrument".

This will take you to the table view of all CaSSIS data which has a filter menu on the left. Note you will not see browse images on the latest data files which are displayed at the top because browse images are only displayed after the 6 month proprietary period.

If you don't want to look at the Housekeeping (HK) files you can uncheck the (HKnumber) boxes in the filter menu and re-do the search using the button at the bottom of the filter menu. Note the HK numbers here refer to the different HK packets downlinked from CaSSIS. Each packet type is stored as a separate data file.

Using this filter menu, you can also choose to look at only calibrated data after expanding the "Processing Level" menu, a time range, and/or all versions. By default only the most recent product versions are displayed.

Isolating an Image

CaSSIS images are split into tens of framelets. Furthermore these tens of framelets exist for each of typically 3-4 filters and then this can be doubled by having Raw and calibrated data. Hence a single image can be represented by hundreds of products.

The easiest way to do this is to use the CaSSIS UID which is within the product identifier and is also known as the logical identifier (LID). Almost all advance CQL queries will use the product identifier.

As this is beyond what the filter menu can do, an advanced search is required. Click on the "advanced" tab on the top of the filter menu. Note the filters set up in the basic menu are not lost, the two tabs work together. You should then see the figure below:

What you get is the "common" advanced search. We are currently working on introducing better mission specific searches. For CaSSIS we have already introduced the ability to isolate by filter. If you click on ExoMars you will see:

Here you can choose any number of filters. Note "multiple' denotes a particular calibration mode where the whole array is read out as a single image.

CQL Search

In the advanced search type:

  • logical_identifier like '%UID%' for example: logical_identifier like '%277775256%'

TIP: The correct quote marks have to be used, if no results are being returned check this or try copy and paste from here.

Now the observation with CaSSIS UID=277775256 has been isolated. You can add a filter to the query through the cql e.g.

  • logical_identifier like '%pan%277775256%' or
  • logical_identifier like '%pan-277775256%'

This Product Identifier/Logical Identifier filter can also be used to isolate calibrated vs raw if this hasn't already been done in the basic menu. 

To see a specific version:

  • version_id = '1.0'

To see a specific orbit e.g. orbit 12488:

  • logical_identifier like '%-12488-%'

Mosaics

CaSSIS mosaiced images are only at the calibrated level and have filenames/product identifiers ending with "-sti". To find the stitched images try:

  • logical_identifier like '%sti%' (for stitched)

  • logical_identifier not like '%sti%'  (for unstitched)

Putting these things together you can now get a list of single observations in the PSA by searching on CaSSIS science plus processing level calibrated in the basic search, identifying a single filter such as PAN (present in most observations) in the ExoMars advanced search and making a CQL query for stitched data.

Expanding Browse Images

To get a better view of any image either click on the browse image then click on the chain link button in the next screen or go to the image gallery view using the gutton at the top of the screen next to the table view, click on the image and again click on the chain link button for the full scale image.

Further information on the advanced operators can be found by clicking on the question mark on the top right of the CQL SEARCH box.

Identifying Stereo Pairs

Currently it is not easy to identify stereo pairs. In future the new observing_mode attribute will be put in the PSA database so that 'stereo' will become a search term which can be used in the advanced search. Before this feature is enabled the following steps are advised:

  • Filter by CaSSIS science, plus calibrated, stitched and one filter typically 'pan'
  • This will give a list of calibrated observations in a table
  • Use the download function, 'Save table as ASCII or CSV'
  • Search the dowloaded files for consecutive UID's

Here is an example:

  • cas_cal_sc_20200120t022402-20200120t022419-pan-556587978-sti
    cas_cal_sc_20200120t022317-20200120t022334-pan-556587977-sti

Note here 'pan' is advised because this filter is used in most observations.

Geometrical Searches

Currently geometrical searches are not yet supported for CaSSIS. The Mars Map View Interface due to be released in autumn 2020 should support this in spring 2021. Additionally in spring 2021 the geometrical search in the filter menu will also be enabled for CaSSIS.

Downloading Data

There are two ways of downloading data either directly or via the download manager. For both methods products need to be selected first using the tick boxes in the table. Note the 'select all' button only selects all products on the page being viewed so to download multiple pages the select all needs to be checked on each.

Once the data are selected the download button on the top right of the screen will then create a popup with the option of 'Download' or 'Send to Download Manager'. If the latter is chosen the number of products selected are shown as in a blue rectangle above the download view button on the top left. Clicking outside the popup will dismiss it. Using the download manager you can additionally select calibration files and documents for your download.

FTP

For large downloads the PSA also offers an FTP server at: 

Here the data are organised by data_level collection, mission phase, subinstrument, orbit range and orbit.

How To View and Start Interacting with the Data

PDS4 Viewer

The easiest way to view the CaSSIS data is to use the PDS4 viewer from the Small Bodies Node. This can be downloaded from 

Note: The PDS4 view can be used to quickly convert the data into a PNG image. Simply open the image viewer click on image then from the file menu 'save image'.

Converting To TIFF or another Format

The data can be converted to TIFF using the PDS transform tool. This can be downloaded from:

Once installed, the path to the parent directory will be setup, but this is included in the installation instructions: A typical call from a Unix based terminal would be:

  • ./transform cas_cal_sc_20200321T105450-20200321T105507-PAN-558123008-sti.xml -f tif

Note:

When calibrated data is transformed you will see a black image due to the low values in the calibrated data. 

PDS4 Tools

Not all operating systems are yet supported so instead you can use the Python tools which form part of the viewer back end to read in and display the data manually. The tools can be found at

and documentation at:

To get started using these tools with CaSSIS data here is an example Jupyter Notebook and associated data file:

Where to Find Out More

A detailed description of the CaSSIS data and how it is produced is in the EAICD. The EAICD can be downloaded from the PSA GUI using the download manager or it can be accessed directly from ftp using:

  • ftp://psa.esac.esa.int/pub/mirror/ExoMars2016/em16_tgo_cas/document

The latest version of the detailed user manual for the PSA can be downloaded from:

More information on the CaSSIS instrument can be obtained from:

If further help is required please contact the PSA Helpdesk (psahelp@rssd.esa.int) or Tanya Lim (tlim@sciops.esa.int)




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