Monday, November 6, 2017

New RADARSAT-2 images! Looking good!

Good news,

Earlier this year, Catherine and I submitted a SOAR-E proposal to acquire new RADARSAT-2 images of salt diapirs. Our original intent was to get images of halite salt diapirs in Iran to compare with our anhydrite diapirs on Axel Heiberg Island. However, we weren't able to get an images over that target site, and we needed to rethink our plan of attack. Instead, we submitted a request for four additional images over Axel Heiberg Island. One of these was over Stolz diapir, where we found halite in the field.  Of our four requests, only two were granted due to RADARSAT-2 targeting conflicts. Fortunately, Stolz diapir was one of them! The other image we received is a bit north of Expedition diapir, which will provide insight into some of the discrepancies between the ASTER TIR predictions and the Harrison and Jackson field mapping.

Like with previous images, I extracted the circularly polarized data in PolSARPro, and produced terrain corrected circular polarization ratio images in SNAP.  I'm pleased to say that they look great!

Here they are:

Images acquired Sept. 26, 2017 over Stolz and Whitsunday Bay diapirs.
Above, annotated HH-Intensity image. Below, CPR image. 
This site was our first priority for the SOAR-E proposal, so I'm pleased it was one of the 2/4 we received. We visited Stolz and Whitsunday Bay diapirs during the 2017 field season, and samples were collected at each. Stolz diapir is where we collected samples from a halite outcrop, and has the extensive perennial springs deposits at its base. The CPR-bright spot between Stolz and Whitsunday Bay diapir to the slight west corresponds with a salt diapir we passed in the helicopter traverse between sites - I'm not sure if it has a name.

Images acquired Sept 30th, 2017. Above, annotated HH-Intensity image showing where Harrison and Jackson (2014) 
mapped salt diapirs, in contrast to where we observed salt signatures in the ASTER TIR images. 

This site was targeted in attempts to discern the discrepancy between mapping methods. This area is subject to significant glacial coverage over the northern half, and it is likely that glacial coverage obscured the TIR signature over Expedition and Thompson diapirs. We also now have repeat coverage over Colour Diapir, which is one of the sites visited during the 2017 field season. I'm not convinced it extends as far to the west as Harrison and Jackson show. I'll need to recheck our field images.

Now here is what they look like with the 2016 images:

The Arctic DEM supports the hypothesis that the northern half of the Sept 30th image is obscured by glacial coverage

Notably, look at Whitsunday Bay diapir - it is REALLY bright in the radar image. It jumps out way more than the other diapirs. I thought for a moment that could be from early snowfall, but note that there doesn't appear to be much snow over the glacier to the west. I'll consult Landsat images shortly.

The new data is quite promising, too! Previously, the average CPR value (per pixel) over salt diapirs and secondary salts were 0.40 and 0.26 respectively. Now, once we include the new data, the average values are 0.52 for the diapirs and 0.23 for secondary salts. I'm really pleased that the new data has increased the spread between the diapirs and secondary salt deposits.

Now, on to writing, writing writing! And some XRD. But mostly writing.

RADARSAT-2 Data and Products (c) MacDonald, Dettwiler and Associates, Ltd. (year of acquisition) - All Rights Reserved. RADARSAT is an official trademark of the Canadian Space Agency.

Harrison, J.C., Jackson, M.P.A., 2014. Tectonostratigraphy and allochthonous salt tectonics of Axel Heiberg Island , central Sverdrup Basin , Arctic Canada. doi:10.4095/293840

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