A sample PlanetServer search and analysis walkthrough is presented. It uses available clients. It is useful to read and try out the basics of the classical client and to familiarize with the new “neo” client. In case of problems, questions, please get in touch or join the planetserver-users google group.
We are grateful for the kind support of Jessica Flahaut (VU Amsterdam).
1. Data search
Data search has been improved progressively on PlanetServer. Pan & Zoom is aided by Regions of Interest (ROIs) or direct access to a certain CRISM observation.
1.1 Using the classical client
The classical client has, in addition to direct URL access, the possibility of searching a certain area, among those ingested so far (growing). E.g. see post on ROIs and their expansion.
1.2 Using the neo client
The “neo” additional client of PlanetServer has a built-in search function based on available ROIs and latitude/longitude range
1.2.1 Nili Fossae
After selecting Nili fossae from the search window or bar (respectively on neo and classic client), the current CRISM hyperspectral coverage is visible:
zooming in to a certain region
and selecting the interest scene
brings up the interface on neo client (the image below shows that the client works also on a small laptop screen, although a larger widescreen monitor is to be preferred):
while the classical client would show
1.2.2 Mawrth Vallis
Mawrth Vallis, another area with clear spectral signatures of certain minerals, could be explored in a similar way.
the CRISM observation and analysis page (neo client) would be:
Similarly, on the classical one:
1.3 Using Direct URL
A certain CRISM product/scene can be directly accessed, from its PRODUCT ID, with a direct URL,in addition to a variety of ways using Desktop GIS or Google Earth, e.g. using shapefiles or .kml files pointing directly to a certain CRISM observation (classic client).
The CRISM observation FRT00003E12 would then be reachable through the URL:
VNIR for Nili Fossae:
having the same effect of browsing + searching a certain product.
The very same for Mawrth Vallis would respectively be:
The naming conventions of CRISM data products is also explained on documentation inked from the Direct Access post.
2. Data inspection, analysis
The basic functionalities of PlanetServer are similar among clients (Basics on 101 post). Also, the PlanetServer console, although not strictly necessary for this walkthrough, can be used for enhanced or faster analysis (on both cients).
A single band can be visualised, e.g. Band 234 (2.54 µm), selecting from the Table of Contents for a single band (highlighted), for the case of Nili Fossae.
the same could be done for Mawrth Vallis:
2.2. RGB with bands
2.2.1 Nili Fossae
Red-Green-Blue color combinations can be perfomed and visualized using the Table of Contents for each CRISM observation (both clients).
For example, a classical false colour composite can be created using R =band 234 (2.54 µm) - G = 82 (1,51 µm) – B= 14 (1,09 µm):
R – 2.54 µm –> Band234
G – 1.51 µm –> Band82
B – 1.09 µm–> Band14
paying attention to the fact that the channel tab in the Table of Contents should be on “IR” and not “VNIR”.
One can also type in the RGB fields by hand, e.g. “Band234″ or any other band number, for easy and quick use.
the process above is also repeated in this video: http://www.youtube.com/watch?v=C3OsRL5yf4I
To reproduce, e.g. Figure S1a from Ehlmann et al. 2009 (DOI: 10.1126/science.1164759) one could use this band combination:
“false color composite with R: 2.38, G: 1.80, B: 1.15 um”:
R – 2.38 –> Band211
G – 1.80 –> Band123
B – 1.15 –> Band24
as visible on: http://www.youtube.com/watch?v=yGAsaB7DqJk
2.2.2 Mawrth Vallis
The same R =band 234 (2.54 µm) - G = 82 (1,51 µm) – B= 14 (1,09 µm) colour composite for the CRISM observation over Mawrth Vallis would look like:
2.3 Summary products
2.3.1 Nili Fossae
Visualization of Summary Products (SP) is a powerful tool to obtain indication of surface compositions.
e.g. for the very same CRISM observation, the SP “olindex” or “olindex2″ indicate the presence of Olivines (see Pelkey et al., 2007. DOI: 10.1029/2006JE002831). Summary Products can be accessed from the TOC, in the rightmost tab:
For example, the following triplet is of particular use for this scene in Nili Fossae:
Red = OLINDEX2 indicates the presence of olivines
Green = BD2500 indicative of carbonates
Blue = D2300 - indicates Fe/Mg phyllosilicate
OLINDEX2 when selected and the “greyscale” options from the TOC chosen, would look like:
A high value of the OLINDEX2 Summary Product would be indicative of the occurrence of Olivines within the bright area, to be then further investigated.
2.3.2 Mawrth Vallis
Analogously, for Mawrth Vallis, the following Summary Products are of use to start with:
Red = D2300 indicates Fe/Mg phyllosilicate
Green = BD2200 (or 2210) – indicates Al phyllosilicate or hydrated glass
Blue = BD1900 (or BD1900R) - indicates hydrated sulfates, clays, glass, or water ice.
The D2300 SP, indicative of Fe/Mg phyllosilicates, would be:
compared with a grayscale view of one of the IR channels cube:
In a colour combination of D2300, BD2200, BD1900, Fe-rich phyllo should appears in red, Al-rich in green.
For comparison, one could look at the static summary page for the observation, e.g. ir_phy - Hydroxylated silicates.
2.4 Spectral analyses
2.4.1 Nili Fossae
Theme: Olivines, Carbonates, Clays
Sample of reference publications:
Mustard et al. (2008) Hydrated silicate minerals on Mars observed by the Mars Reconnaissance Orbiter CRISM instrument. DOI: 10.1038/nature07097
Ehlmann et al. (2009) Orbital identification of carbonate-bearing rocks on Mars. DOI: 10.1126/science.1164759
Spectral libraries: Phyllosilicates, Carbonates
RGB visualisation and summary products are highlighting the differences in composition across the CRISM scene, e.g. bands 234,82,14 as RGB.
Sampling relevant points across the hundreds of bands in CRISM IR (with an underlying WCPS query) provides access to additional information. Spectra can be collected on desired points with the Spectrum button:
The three spectra show already different shapes, indicative of variability of the surface’s nature. Multiple spectra can be collected and each appears with a different colors, reflected both in the collection point (map) and in the spectrum plot (diagram widget).
In this case, the 4 spectra (and their relevant sampling point) reflect different surface units, roughly:
Purple: a rather featureless dusty spectrum (to be used as reference for ratios, see next section)
Blue: Fe-Mg rich phyllosilicates (clays) ((1.9 and 2.3 μm bands)
Green: Olivine (wide 1 μm absorpJon)
Red: Carbonates (2.3 and 2.5 μm bands)
the process can be visualised on: http://www.youtube.com/watch?v=uxSzR90svcQ
Performing a ratio of 2 different spectra (e.g. a feature-rich one as 1st click divided by one flatter / featureless in the same scene, as 2nd click) can help highlighting differences and the presence/magnitude of existing features, band depths, etc. The Spectral Ratio button is to be used:
and the resulting spectral ratio, using as reference the flat spectrum (indicated as purple in the previous map) can enhance adsorption bands. In this case, the unit indicative of carbonates (2.3 and 2.5 μm bands).
Spectra can be compared qualitatively with spectral libraries, which are included in PlanetServer (see info on CRISM web site and PDS CRISM spectral library pages).
Laboratory spectra can be loaded from within the diagram window, e.g.:
The resulting spectral overlay allows for visual band identification.
An example of the process is provided on: http://www.youtube.com/watch?v=PcULp5mFA14
2.4.2 Mawrth Vallis
Sample of reference publications:
Loizeau et al. (2010) Stratigraphy in the Mawrth Vallis region through OMEGA, HRSC color imagery and DTM DOI: 10.1016/j.icarus.2009.04.018
McKeown et al. (2009) Characterization of phyllosilicates observed in the central Mawrth Vallis region, Mars, their potential formational processes and implications for past climate. DOI: 10.1029/2008JE003301
Wray et al. (2008) Compositional stratigraphy of clay-bearing layered deposits at Mawrth Vallis, Mars. DOI: 10.1029/2008GL034385
Spectral libraries: phyllosilicates
Analogously, spectra can be collected across a sample CRISM observation in the region of Mawrth Vallis. In this case, the RGB composite is (R, 2.53 mm = Band234; G, 1.51 mm = Band82; B, 1.01 mm = Band14).
Blue: Neutral, feature-poor spectrum to be used for ratios
Green: Fe-Mg-rich phyllosilicates (clays) ((1.9 and 2.3 μm bands)
Red: Al-rich phyllosilicates (clays) (1.9 and 2.2 μm bands)
Performing a ratio, e.g. using the Al-rich phyllosilicates unit and the feature-poor reference point, will enhance, for example, the bands at 1.9 and 2.2 µm. Comparing with spectral library items can be performed as well:
A new editing capability is present in the neo client. The following requires the use of http://neo.planetserver.eu
A user should log on the client, from its toolbar, on the upper right:
and fill in his/her credentials [for the time being, the registration is not open automatically, due to hardware constraints]
one could reach the same CRISM observation, e.g.
Feature (point, line, polygon) editing can be performed using the detached small toolbar just below the main PlanetServer toolbar:
In order to enable the editor, one should press on the “editor” button on the toolbar
a feature, such a polygon (3rd drawing icon from the left) could be created on the map:
for example highlighting a certain area:
the polygon, when editing is finished, changes colour:
and it can be saved on a PostGis database with the button “save”.
The features are then saved with each user. A dialog confirm the save operation.
Features can be deleted individually or cleared totally:
When visiting again and logging in, saved features are loaded automatically.
Future developments might include automatic location of edited features (currently the user should navigate to the mapped area/CRISM observation, if logging in in a completely new browser session), etc.
Also, search functions for mapped polygon or multi-user collaborative features might be added as well.
4. 3D view (X3D)
X3D, developed for all Services of Earthserver, is integrated in the web client and it offers a 3-dimensional rendering of the CRISM observation of choice draped on digital topography.
The default topographic base is MOLA gridded laser altrimetry (Mars Orbiter Laser Altimeter, on board NASA MGS), e.g. for the case of Nili Fossae, the toolbar DTM option is MOLA only:
When higher resolution topography is available, such as in the case of MSL landing site Gale Crater, the user could choose it as a base for draping imagery, starting from a CRISM observation, such as:
The X3D button on the toolbar loads the 3d viewer:
producing an empty 3D viewer
which should be populated by pressing the “create scene” button (lower right):
When multiple topographic sources are available, such as for Gale crater, they can be chosen beforehand from the toolbar. E.g. after choosing Gale in the search window, the HRSC DEM can be used as height source. This can then be used for the 3d visualiser.
Once the base DTM is chosen, one could just select the desired CRISM observation and follow th e same procedure, launching the X3D client. The CRISM dataset is then draped over HRSC DTM rather than lower resolution MOLA.
More high-resolution (HRSC stereo-derived) topographic models are going to be added to PlanetServer in the near future.