Wednesday, September 6, 2017

Comparisons between features in Yellowstone and on Axel Heiberg Island

Hi hi!
Eclipse, 10:22 MST, I took this
through a telescope

I’m writing to you after a phenomenal family vacation I took with my parents, aunt and uncle down to Idaho and Wyoming. The main destination – the totality zone for the eclipse! The eclipse was indeed a very breathtaking, magical experience, but today I will be writing about some of the geology we saw. While passing through Idaho, we stopped at Craters of the Moon National Monument. We briefly visited with Gavin, Kevin, Raymond, and Mike who were a bit knackered after a day of strenuous fieldwork. I won’t write much more about those lava flows, because Gavin has written about them in stylish detail.After Craters of the Moon, we drove into Wyoming and visited what must be a geological, volcanic mecca – Yellowstone National Park. Now, I could write for pages about the geology of Yellowstone, because it is such an exciting, unique place full of epithermal wonders. For this post, I’m going to focus on two features that seemed to show some parallels to what I saw on Axel Heiberg Island. (But you can see all my photos here!)

First are a lot of ignimbrites around the park, whose violent eruption triggered the massively catastrophic caldera collapse 640,000 years ago. Also known as
ash-flow tuffs, ignimbrites are a type of pyroclastic flow deposits characterized by high abundance of ash-sized (<4 mm) particles and pumice.  The scale of eruption required is enough to partially or fully empty magma chambers. The dramatic exodus of material substantially decreases the internal pressure of the chamber, often resulting in caldera collapse if the chamber roof is no longer sufficiently supported. The top of the magma chamber erupts out and is deposited first, so the ash-flow tuff sequence represents the inverted order of the magma chamber’s internal fractionalization.  The layers in ignimbrites can be divided into pyroclastic flow units from multiple eruptive pulses. A typical ignimbrite sequence contains a basal layer with reverse graded pumice and lithic clasts. Above the basal layer, flow units have density separated clasts: pumice is light and floats to the top, showing reverse grading, whereas denser lithic clasts are normally graded. Ash-flow tuffs thin out and have fewer clasts away from their source. If the flow units cool together, they form a compound cooling unit. Sufficiently hot and thick ignimbrites fuse and solidify from partial or complete welding. Welding occurs when hot, pliable pumice clasts flatten under overburden weight and sinter together, giving them a glassy appearance (Francis and Oppenheimer 2004).
Now you are no doubt wondering what on earth a explosive, caldera-building volcanic unit has anything to do with salt diapirs in the Arctic.  Genetically, nothing. But morphologically? Take a look:
The walls of this river-carved valley are jagged and karstic, looking a lot like what we saw at Stolz and Wolf Diapirs.
This looks a lot like that pseudo-karstic topography we saw in the Axel Heiberg Diapirs. The reason is simple. Ash, like salt, is softer than other types of rock. Therefore, it erodes away more readily than the surrounding units and forms jagged peaks. In fact, because ash-flow deposits are soft the Fremont First Nations used faces of ignimbrite for wall carvings in Utah.  I thought this was neat, and worthy of sharing. I imagine that ignimbrite exposed in valley or canyon walls would look very similar to salt diapirs in synthetic aperture radar, which further demonstrates the need to combine different orbital datasets paint a full picture.
Second are the hot spring travertine deposits, like Mammoth Hot Springs.  The mechanism that forms these deposits in hot springs at Yellowstone is like the perennial cold springs in the Arctic. In Mammoth Springs, geothermally heated ground water passes through limestone via a fault, and leaches out calcium. The calcium-rich water upwells to the surface and deposits calcite in the form of travertine as it cools.  

Mammoth Hot Springs has produced the largest known travertine deposit

Seismic activity alters the spring flow paths, enabling expansive terraces to form 

On Axel Heiberg Island, the waters that form Lost Hammer Spring are thought to be passing through subsurface extents of the Wolf Diapir, thereby passing through halite and anhydrite and leaching out sodium and calcium. Subsequently as the spring flows over, the deposits at Lost Hammer are halite, calcite, gypsum, thenardite and mirabilite (Battler et al. 2013). Despite Mammoth springs being a hydrothermal system, and Lost Hammer Spring being a perennial cold spring, I find it interesting that both sites are formed the same way.
Lost Hammer Spring, seen from above

The edge of Lost Hammer Spring, where salt-rich water has overflown and precipitated

In a week and a half, I’m going to the Space Generation Congress and the International Astronautical Congress in Adelaide, Australia! If I find some downtime, I’ll try to provide some short updates here, but I’ll definitely be tweeting about the conferences!
Battler, M.M., Osinski, G.R., and Banerjee, N.R. 2013. Mineralogy of saline perennial cold spring on Axel Heiberg Island, Nunavut, Canada and implications for spring deposits on Mars. Icarus 224: 364–381. doi:10.1016/j.icarus.2012.08.031.
Francis, P. Oppenheimer, C., 2004. Volcanoes Second Edition. Oxford University Press.

Tuesday, August 8, 2017

Axel Heiberg Adventures Part II

                Hello, hello, and welcome to Part II of our Axel Heiberg field adventures! As mentioned last post, we moved campsites about half-way through the trip. The plan was to move from Lost Hammer Spring to South Fjord Diapir. South Fjord is the largest salt dome on the island at a monstrous 5 km diameter! We were to make the move in three trips by helicopter. Oz and I would go first with our personal tents and some other essential gear, the helicopter would return and pick up a net load (literally, in a hanging net) of other gear including the fat bikes, and then on the third trip would bring Mike and Mark with the communal tent and the remaining gear. So Oz and I took off, needing to scout for a place to land that would be safe, accessible, and geologically interesting. But in a 5 km-wide mountain of continually rising and crumbling salt, what could not be interesting?

Until we got there.

...
Oh.

That’s, um.  Hmm.

Well, at least we can confirm South Fjord Diapir has rough surfaces.
There is too much snow! We can’t possibly land here! Oz is shocked – it is mid-July and South Fjord Diapir is a winter-wonderland. He said that he visited this site in late June some-years ago, and there was nowhere near this much snow. This has some interesting implications for remote sensing work. Snow and ice can heavily influence radar response – what if South Fjord dome was blanketed in snow when our radar images were taken? I resolve to check Landsat images taken around the dates our radar images have been taken. I have done this since returning – it does look like one of our six images might be affected – perhaps I should mask out the ice and snow and redo the radar zonal statistics extraction!

What do we do? We flew around the dome for a bit, taking pictures while deciding where our backup camp will be. Remember that helicopter time is a valuable resource, so we need to decide quickly. Oz asks if there is a diapir near the end of Strand Fjord. I recall that there is, but I don’t know the distance to it. As we begin to fly over there, I pull out the field laptop that I had in my backpack. I’ll admit, I felt pretty cool flying in a helicopter while measuring distances in ArcGIS to make quick decisions where to land. I determine that Strand Diapir is approximately 6 km from the shoreline, and we deem this close enough to hike to.  We’re off to land in Strand Fjord!

And oh, what a beautiful campsite it was!


Icebergs in the Fjord, a low fog is rolling through. The dark rock unit is an folded igneous sill.
The brown rock is gullied the surface has undergone solifluction.
Strand Fjord, near our campsite.
The sandy banks have compositional layering.
I honestly think this is the most wonderful place I’ve ever camped. We had glaciers and ice bergs and beautiful sharp mountains with intense solifluction. It was beautiful. I did some soil sampling between our camp and the Fjord on one of our off days. 
Again, we saw patches of precipitated salts. Interestingly, these salts tended to be concentrated along the rims of wet/dry sand boundaries. The whole fjord area shows up in the TIR images as having VERY STRONG gypsum/anhydrite signatures, all deriving from the nearby Strand Diapir. Mike, Mark and I went on a hike to visit the northern half of the diapir exposure one day. 

The inland-area of the Fjord appears to be a glacially carved U-shaped valley, so Strand Diapir is split into two main outcrops across the valley. The salts in Strand Diapir are also interacting with some volcanic intrusions, causing some beautiful iron staining.


Behind me is the glacier that carved the U-shaped valley and provides the meltwater for the river.

The brilliant colours are from oxidation reactions between igneous rocks and the diapir.
The igneous rocks provide the metals, the anhydrite provides sulphur.
A reoccurring theme, the outcrops show some exposures of intact rock salt, but the majority of the surface has weathered into the highly vuggy gypsum crust that is characteristic of the Axel Heiberg Island anhydrite diapirs. Part way up the valley wall, the anhydrite is interbedded with what I think is limestone. I haven’t exampled the sample yet, but the dark colour and texture looks like a carbonate and past literature states that limestone is commonly interbedded with the Otto Fjord Formation salts. On a regional scale, the diapir material is stratigraphically overlying the orange stained unit, which I think is a volcanic sill, and has since undergone synclinal folding.

Flying in a helicopter never gets old
Something that I really appreciated this trip was being able to finally investigate the mystery of the radar-dark bright region, mapped as Isachsen Formation (quartz sandstone with some igneous intrusions). As a weather front was rolling in, our helicopter pilot asked if we wanted to make any last quick visits. I gave him the coordinates at the centre of the feature – the peak of a broad mountain range. He looked westward, and observed that that was where the storm was the thickest, and he wouldn’t be able to land there. Nonetheless, we headed that way along the coast, wary of the thick clouds in the distance. The very peaks were shrouded in clouds, but he asked if seeing the sides were enough. Elated to be there, I said yes, and to my delight we made a full perimeter tour around the feature before heading back to the safety of our campsite. Many photos were taken, and the verdict is that these slopes are COVERED in cobble-sized talus that would effectively scatter RADARSAT-2’s 5.6 cm radar beams. Since these are also high elevation peaks, snow and ice is admittedly also a possibility. I’m going to check the Landsat images soon to investigate. Sadly because we couldn’t land I wasn’t able to sample, or get good scaled photos. -sobs-
In addition to the fist-sized rocks everywhere,
take a moment to appreciate that sweet folding.
Travertine terraces from perennial spring from Colour Peak
Finally, one of the highlights of the trip was scaling the 550 m Colour Peak. Colour Peak has been part of the epitome for my thesis, showing that salt diapirs are radar-rough, whereas the materials that erode off of them and reprecipitate elsewhere are radar-smooth. Mark and Mike spent the day sampling the calcite-rich perennial springs effusing from the base of the mountain. The springs are building terraces of black travertine – the type of calcite that precipitates from cold water springs. 1-3 mm cubic halite crystals lined the edges of the streams. Mike founds some really cool crystals in a small cave – the sample he gave me is decorating my coffee table as I write this. The smell of H2S was pungent, and I found myself craving egg salad whilst down there. 
Oz and I, however, journeyed up to climb the massive diapir.  The best exposures of salt textures were at the top, with the flanks being either covered in soil, talus, or completely weathered and crusty outcrop.  The ascent was tough.  The diapir is steep sided covered in poorly sorted colluvium. The skree contains sand to boulder-sized rocks. We also found some palm-sized fragments of clear selenite crystals amongst the soil patches. I think the anhydrite colluvium and gypsum-rich soil is enough to product the spectral signature seen in the ASTER TIR image downslope of Colour Peak without us needed to appeal to the perennial spring. Because much of the slope material was unconsolidated, our feet were prone to slipping down as we moved upwards. I’m very fortunate that Dr. Osinski is an experienced climber, and I was able to follow where his footsteps packed down the debris.  Frequently we would take a step on what seemed to be solid ground, only to have our foot punch through the weathered gypsum crust into a 20 cm deep vug.  
Rough, steep, the return of slightly karst-y topography.

Close to the summit are outcrops of solid anhydrite or gypsum. Unlike at Wolf Diapir, where the solid salt was powdery and friable, here the salt is crystalline.  Erosional processes are carving the solid salt into points like the rillenkarren seen on halite diapirs and in karstic carbonates. The rillenkarren are smooth at the mm scale, but undulate at the cm scale and would appear rough at C and L-Band SAR. 
Rippled rillenkarren textures on crystalline anhydrite sample.

The sharp, solid salt looks beautiful up close.  Of course, nothing compares to the stunning, beautiful view from the summit!

Yes.

An excellent view across Expedition Fjord,
            and the travertine perennial spring down below

Wow.

The rocks up here are mostly blocky, partially weathered, and the ground is covered in colluvium. Once again we are able to confirm that salt diapirs are rough on the ground, not just in radar.


Very blocky, rough, and sadly too unstable and dangerous to venture farther.
You can see where Colour Diapir ends, and the adjacent mountain begins
based on surface texture alone. 
  Any discussion of Colour Peak would be incomplete without explaining how it got its name. The colluvium also includes rubble and gravel of angular igneous lithologies, including what is ostensibly dacite and diorite. Some of the volcanic material is oxidizing to form gossans. The gossans are dazzling zones of vivid orange, yellow, and brown alteration. These are found in close association with diapirs on Axel Heiberg Island, including North Agate Fjord and Junction Diapir where basaltic intrusions from the Isachsen Formation are altering to form copper and iron sulphides and secondary copper sulphates (Williamson 2011). The calcium sulphates in the diapir provide the sulphur for these alterations to occur. Remember, we saw this same alteration at Strand Diapir!  We collected some samples of yellow rhombohedral crystals have been taken to the lab to for analysis

The journey home was bittersweet. I’m going to miss this place.

And such concludes my 2017 Axel Heiberg adventure.
Elise xx

Tuesday, August 1, 2017

Axel Heiberg Adventures Part I

Okay, now that I’ve had a week to recover and sort through things, I am delighted and excited to share some of my field experiences with you!  July 5th-20th marked a two-week adventure into the Canadian High Arctic. Our goal: Axel Heiberg Island.  This is why this blog is called, “Arctic Resolution” after all! In a sense, this trip is the epitome of my M.Sc thesis because it gave me the opportunity to “ground-truth” all the observations and analysis I’ve been doing remotely up to now. In essence, I got to see what my radar and spectroscopy images look like in person! It was seriously cool to be able to have that opportunity.

If you need to recap quickly what my thesis is about you can watch me explain it in three minutes:


We are trying to see how radar can be used for remote predictive geological mapping. Remote predictive mapping is not only useful on Earth to save time and money – it is often the only way we are able to learn about the surfaces of other planets and moons. The techniques we are developing are important for planetary science, as Earth is the only planet humans like us can go and check in person. Thus the need for terrestrial analogue studies, which is one of the focuses and strengths of the University of Western Ontario’s Centre for Planetary Science and Exploration. My project is largely grounded in economic geology (salt diapirs -> petroleum + ore deposits -> $$$ = 😊), but I like that this project also has potential analogues for radar mapping and is helping me develop skillsets vital to planetary sciences.

So, what did we see?
~~~LOTS OF FUN THINGS~~~


This blog post, for the sake of avoiding rambling on and on, will contain summaries of Part I of our field adventures. About half way through our time on Axel Heiberg we moved campsites from Lost Hammer Spring to Strand Fjord, so I will cover our work done around the first campsite.
We found one of our first scientific findings before the Twin Otter even landed. Remember how I was puzzling over the nature of secondary salts? The strong ASTER thermal infrared spectral signatures for gypsum or anhydrite that weren’t confined to salt domes, but rather in gullies and river floodplains? I was wondering if those signatures were the result of:
               
1. Rubble and gravel of mechanically eroded diapir materials (chunks of salt rock)
            2. Precipitated salt minerals that geochemically dissolved out through water flow

Number 2 is our winner! Just looking out the Twin Otter windows the secondary, precipitated salt is abundant and widespread. 
Salt minerals precipitating in gullies and floodplains
Of course, we confirmed that it is salt minerals on the ground later, and have collected many samples that we will XRD to identify, but it is incredible that we solved one of our biggest field objectives before even landing! These hillslopes and floodplains are predominantly radar-smooth soils, with some colluvial or fluvial pebbles and cobbles.  The salt bearing gullies and stream channels contain larger pebbles, cobbles, and sporadic boulders, but I think these features are too localized to affect the CPR images at the scale of RADARSAT-2 or PALSAR-1 multilooked CPR image resolution. The salt encrustations are <1 mm in thickness on the surfaces. Although boulders and cobbles of salt have mechanically broken off diapiric structures, like the flanks of Wolf Diapir, these likely contribute to the rougher radar signatures seen in the CPR images in association with the diapirs. Later, I also found that there are at least two types of salt minerals precipitating: halite, and what is likely gypsum or anhydrite. I discovered the halite using the classic method all new students learn in Earth Science 101 – licking the samples.
However, what sort of surprised us was the weather-dependence of these surficial salts. When we first arrived, on a beautiful, clear, sunny day, these salts were very sharp in contrast against the landscape. When I walked up the stream at our first campsite, the rocks in the riverbed exposed above water were coated in a white crust. Then the rain and snow came. After three days of snow, almost all of the white encrustations disappeared! There were still white patches on the hillslopes and in gullies, but they weren’t nearly as stark as before. After a day or two of the weather clearing up, the white minerals appeared again, almost as abundant as when we arrived. We think the snow and rain dissolved the salt minerals and they were able to precipitated again from the surface water after the ground was able to start drying.
Salt minerals encrusting some rocks on hillslope

Our first campsite was at Lost Hammer Spring. Lost Hammer Spring is a perennial spring, one of many places on Axel Heiberg Island where brines upwell to surface and deposit large precipitated structures of salt. It is entirely possible that the source of the salt in these fluids derives from the core of the adjacent Wolf Diapir, but this has not been conclusively proven. The salt that makes up Lost Hammer is very sodium rich, implying that the groundwater has interacted with subsurface halite (i.e. table salt) (Battler et al. 2013) but no halite has yet been found at Wolf Diapir. The only diapir at which halite has been found is at Stolz Diapir, which we visited and sampled later in the trip. It is entirely likely that many diapirs on Axel Heiberg Island contain halite in their cores, and that this is simply not exposed at surface. Curiouser and curiouser! Halite was even found precipitating in small patches a few kilometers downriver from Lost Hammer. Like the secondary salts, Lost Hammer Spring exhibited a similar wet/dry cycle. Upon arrival to the field site, the Lost Hammer Spring was a dazzling white, but during the snowfall the spring became greyer and muddier. Either the surface layer of salt was exfoliated, or mud was transported onto the spring during the wet interval. 


Not a snow bank, this is all salt! Lost Hammer Spring (aka Wolf Spring) has accumulated an almost 2 m high vent of halite, calcite, gypsum,
thernardite, and microbilite. The shape of the perennial spring changes seasonally, with periods of partial dissolution and reprecipitation

               Wolf Diapir is characterized by having steep slopes and heavy erosion compared to surrounding rocks from the Isachsen Formation and the Invisible Point Member of the Christopher Formation. The contrast in surface texture is sharp between Wolf Diapir and the other formations. Whereas the adjacent rock formation has regularly distributed gravel in soil, the flanks of the Wolf Diapir are characterized poorly sorted very angular colluvium from sand to block sized particles. Two textures were pervasive amongst all the diapirs we visited this trip - solid, crystalline anhydrite, and weathered, heavily altered vuggy gypsum. 
Wolf Diapir. You can see how the surface of the mountain is far rougher and more gullyied than the surrounding hills.


Close up, you can see how heterogenous and blocky the surface of the diapirs are. Broken fragments range from granule to block sized. It is frequently difficult to determine which blocks are in situ or broken

This weathered, vuggy crust is pervasive across all diapirs we visited.


Other intact anhydrite (or gypsum?) has different lithologies across different diapirs.
At Wolf, the crystalline material was very friable (likely still altered) and highly veined with what might be limestone.

A long gully with 2 m high levees made up of large angular boulders runs down the eastern flank of the structure. We mapped this using a portable LiDAR system.
Dr. Osinksi stands adjacent to the 2 m high colluvial levee flanking a prominent gully coming down Wolf Diapir
              On one of our helicopter traverse days, we could visit Stolz and Whitsunday Bay diapirs are located outside of the WABS region, on the eastern side of the island. Right now we don’t have  RADARSAT-2 or PALSAR-1 coverage over these sites, but I contacted a gentleman at the CSA about using our SOAR-E proposal to get some. For now, we are interested in their chemistry and spectral responses. The top of the diapir is encrusted with a thick, weathered crust of gypsum/anhydrite.  The slopes are steep, with large blocks broken off on the flanks and in the valleys. The topography on Stolz Diapir is karstic, with tall, jaggaed pillars of eroded diapir material.
In some places, the erosion characteristics of Stolz Diapir appeared karstic in nature.
We saw some of this later on at Colour Peak as well.
Like Wolf, Stolz Diapir is very rough and blocky.
                Large vugs within and beneath the altered crust and small dissolution caves run throughout. Two streams run through the structure, converging along the eastern flank. These two streams have different water chemistries and sediment load. One stream has distinctively more halite than the other, and likely runs through Stolz’s halite core. Halite is exposed in outcrop downstream of where the streams converge. Textures within the halite range from white powdery massive structureless to colourless/grey clear crystalline halite with perfect cubic cleavage. Some areas of crystalline halite are green tinged from localized yellow spots which may be endolith colonies.
Dr. Osinksi stands in front of large halite outcrop

In certain places, the halite could be seen growing in framboidal bulbs of small cubes

There are extreme, extensive, thick perennial springs deposits downstream.  They are seriously insane. It looks and feels like walking through snow! These salts have varying textures, colours, banding, and crystal structure. Upstream are alternating light and dark grey salts. Downstream by a pool are pure white, snow-like salts with bladed/rod crystal structures. The strength of anhydrite/gypsum over the spring deposits is notably weaker than the signature over the diapir itself, likely because the spring is predominantly formed from precipitated halite or calcite travertine.


Extensive, massive perennial springs! The white and grey is all salt!
Note the differences in colour and texture between the white and grey salts.
Mark sampled each, and so hopefully he'll be able to tell us what they are.


Salt salt salt!  Everywhere! So that concludes the first part of Arctic updates. Stay tuned for part II within the next fortnight.

Tuesday, July 25, 2017

Earth Observation Summit Recap

Last post, I mentioned that I would provide a recap of the Earth Observation Summit in Montreal, June 20-22th. I am very happy to have had the chance to both learn about up and coming earth observation technologies, as well as present my own research at the summit. Admittedly, you, dear readers, are probably more interested in hearing about my Arctic Adventures to Axel Heiberg Island (July 5th-20th), but I haven't quite sorted through my notes and photos from the trip yet to write a blog post about it. Soon! Likely for next week.

I had the pleasure of attending both the Synthetic Aperture Radar (SAR) Workshop and the Summer School. During these seminars, we learned about different applications of SAR, types of hyperspectral remote sensing, and the use and application of unmanned aerial vehicles (UAVs) for research, military, and civilian purposes. Something that really stuck out to me was the level of resolution and detail attainable from hyperspectral analysis. I knew that spectroscopy could be used to differentiate rocks, mineral content, vegetation, and man-made structures as I have done similar classification in remote sensing coursework and for my thesis. But at the workshop I learned that "level three" hyperspectral imaging can be used to differentiate between specific types of plants and roofing materials of buildings. This surprised me, and I'm really impressed by the versatility of spectroscopy, and all the fields it can be applied to. I suppose it makes sense, I mean, if spectroscopy can differentiate between different minerals, why wouldn't you be able to detect different types of plants and polymers? I never thought about it. In a different session, I also learned that the spectral signatures of plants are seasonably variable based on phenological changes. This is intuitive, since plants go through different phases of growing, leave production, and leaf loss, but again, it is something I hadn't thought about.

Before the SAR Workshop, I knew radar had a variety of applications in ground subsidence, natural disaster monitoring, and military intelligence, but did not know the nuances behind how these techniques were applied. Now I have a better understanding of the many Interferometric SAR processing steps for monitoring ground movements, and how RADARSAT-2 is used for naval surveillance in the Canadian Arctic.

My presentation “Polarimetric radar for remote geological mapping of salt diapirs on Axel Heiberg Island, Nunavut” was well received in the Polarimetric SAR Processing session. The session was well attended, and some audience members asked insightful questions about my work. One gentleman asked if we were potentially detecting limestone in addition to gypsum and anhydrite with our Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) spectroscopy and in our radar images because both limestone and gypsum can show similar signatures. This is another case of where radar and topographic information may be useful in differentiating the differences between different rock lithologies based on their morphology and surface textures. I am delighted and honoured to say that my talk won second place for “Best Student Presentation” at the Congress. I am always happy to talk about rocks and satellites, and would love the opportunities to continue to share my knowledge and research in salt diapirism and polarimetric radar remote sensing at future conferences and meetings. Anyone who has been around me in the past few months has probably heard my three-minute thesis half a dozen times as I elucidate new quarry about the wonders of remote predictive mapping.

Over the course of the congress, I had many opportunities to connect and reconnect with colleagues and industry professionals. It was a pleasure to speak with representatives from the Canadian Space Agency again after meeting them last November for the Mars Sample Return Simulation at the University of Western Ontario. I also reconnected with people I had met at the Canadian Space Exploration Workshop whom I discussed the status of the RADARSAT Constellation Mission. Since I've been using RADARSAT-2 data for my thesis, I'm curious about the coverage the Constellation Mission will provide improved coverage over the Canadian high Arctic. I also met one of the Advisory Board members for the Students for the Exploration and Development of Space (SEDS-Canada) for the first time that I had been in contact with through e-mail. I'm currently the Vice-Chair of SEDS-Canada, and working with the Board of Advisors is one of my roles in that.

In summary, the Earth Observation Summit was a very productive meeting. I learned a lot about SAR, which is beneficial to my M.Sc. research work, as well as other methods of remote sensing that has given me a more well-rounded and diverse understanding of Earth observation methods. I met many satellite industry professionals and learned a lot about Canada’s contributions to the space industry. This opportunity has given me a broader global understanding of space systems sciences. I look forward to being able to apply what I have learned at the Summit towards my future career aspirations in planetary mission work and space administration.

Soon you will hear about my Axel Heiberg adventures.  Soon.

Wednesday, June 14, 2017

PALSAR - Hiccups Part II

I'm very excited to say that next week I have the pleasure of attending the Earth Observation Summit in Montreal!  The summit is a combination of three meetings: the 38th Canadian Symposium on Remote Sensing (CSRS), the 17th Congress of the Association QuĂ©bĂ©coise de TĂ©lĂ©dĂ©tection (AQT) and the 11th Advanced SAR (ASAR) Workshop.  My main purpose in attending is for the ASAR Workshop, but I am also very keen on learning all about the cutting edge remote sensing techniques and satellite technologies!

I have a presentation in one of the sessions on Advanced Polarimetric Methods. Mike and Hun will also be attending, and they have talks in the Geology session (wah! I'm geology, too! But my topic fits in either session :) )  Next post, I'll tell you all about the cool things I learned!

In preparation for my talk and our upcoming field season to Axel Heiberg Island, I was going through some of my data with a fine picked comb.  Remember those PALSAR Hiccups I was having before? It turns out things are a bit worse than I previously thought!  Not only are the images poorly registered (i.e. they don't line up with the other maps properly) but there is also some severe distortion to a process called 'layover', which is a common, unfortunate challenge with radar imaging. I wrote a little bit about layover in a previous post last year.  Usually terrain correction helps lessen the distortion.

Compare these HH-Intensity image pairs:

Figure 1 Two images of South Fiord Diapir. Above, RADARSAT-2, water is masked out. Below, PALSAR-1 with water included.  Note how the shape of the dome is distorted in the PALSAR image, with a thick white line on the eastern margin.


Figure 2: Above, RADARSAT-2, below PALSAR-1. Again, water is masked out in the RADARSAT but not the PALSAR image. Pink outlines delimit salt diapirs as identified in  other spectral datasets, including (west to east) Surprise Central Diapir, Bastion Ridge Central Diapir, and Glacier Fiord Diapir. Notice how the mountains are more defined and '"3D" looking in the top image, but appear almost sideways or overturned in the lower image. Additionally notice how combination of the layover distortion and poor image registration results in the pink outlines being offset from the actual features.

The cause for this distortion is the incidence angle. The incidence angle is the angle between the radar beam and the normal (perpendicular to) to the surface (Figure 3).  

Figure 3: Illustration of angle of incidence, from Wolfram

For the RADARSAT-2 images the incidence angle is ~40▫, where as the PALSAR-2 images have an incidence angle of 21.5▫.  For a flat surface, this wouldn't be much of a problem.  However, as shown in Figure 2, Axel Heiberg Island has a lot of hills, mountains, and diapirs!  The angle of repose for most materials is around 30▫, and that can be less for bigger blocks.  It is likely that a lot of the mountainous areas are sloping close to the incidence angle of the PALSAR-1 images. This means that the radar beams are inflicting the surface almost perpendicular to the mountains, making them look flat!  And oddly sideways!  To help me visualize this better, I made some sketches and set up a physical model using my bus pass, an external hard drive and a pen, but hopefully you won't need to do that. 

There are two main types of slope angle effects, forshortening and layover. Most radar images (unless you are looking at extremely flat terrain!) will experience these to some extent. The effects are exacerbated in mountainous areas, and with smaller incidence angles. Recall how radar works - we are sending a beam to a surface, and measuring the amount that bounces back.  The amount of time it takes for the beam to bounce back can affect its position in the image, so if a radar beam is taking different amounts of time to reflect off of different parts of an object, that can affect what the object looks like in the image.

Foreshortening occurs with a radar beam reaches the bottom of a slope feature before the top. In foreshortening, slope facing the radar beam will appear "shortened" in the resulting image. The lower image in Figure 1 shows foreshortened western flank of the diapir dome.  Layover is similar, but occurs when the radar beam hits the top of the slope before the base.  This makes it look like the sloped feature is tilting towards the radar position. The lower image of Figure 2 is a better example of layover, because it looks like those mountain ranges are tilted sideways towards the east (I think - that's what it looks like to me, but I'm still learning how to recognize these effects. :) )

Ultimately, these distortions have shown that not all of our PALSAR-1 data is reliable.  I noticed that a lot of the salt polygons were misplaced from the distortions.  However, I am happy to say I was able to perform a quick band-aid solution.  I went through each of the polygons and did a quick visual assessment to see if the radar looked reliable. I manually moved some of the polygons in ArcGIS so they would be overlying the right features even if the shapefiles aren't registered the same. This has given me enough patched-up data to still present some PALSAR-1 results at the conference next week, but it is a short term solution until we either re-register the data, or scrap it.

So, the 'new' results show that the salt diapirs more rough in PALSAR-1's L-Band than in C-Band.  In C-Band, the CPR average values are ~0.4, but in L-Band they are ~0.6! The non-diapiric salts have similar signatures.  In C-Band non-diapiric salt has CPR ~0.21, and in L-Band it is ~0.23.  Previously we thought there were some radar-rough areas of non-diapirc salt in L-Band, but I have confirmed those were registration issues.

This is still good, and we can work with this!

I'll let you know how the Earth Observation Summit goes!

For more information on radar slope effects, this page is awesome: 

RADARSAT-2 Data and Products (c) MacDonald, Dettwiler and Associates, Ltd. (2016) - All Rights Reserved. RADARSAT is an official trademark of the Canadian Space Agency.

Monday, May 29, 2017

Back to the Arctic: An anomalously radar-rough area

Hi, hi!

For this week's update, let's return up north to Axel Heiberg Island, NU.  Recently, I've been revisiting my radar and spectral images in preparation for our upcoming field season. In July, four of us will be visiting the island to ground-truth what we've been seeing in the satellite imagery, with a specific focus on the salt diapirs I've been studying. This will help us better understand the surface texture of the diapirs, how rough they are, and why they are producing the signatures we see in radar.

Part of the Canadian High Arctic, including Axel Heiberg Island, and most of Ellesmere Island. Boxed represents study area for Elise's research. Image credit at bottom right.

One area, not made of salt, is quite curious. There is nothing abnormal about it in the true-colour satellite imagery.

Overview of study area on Axel Heiberg Island. This "wall-and-basin structure" contains a high abundance of salt diapirs. Image credit same as above. Box outlines "weird" area.

But yet it appears very rough in C-Band radar.  More rough than the diapirs, even! Check it out:

RADARSAT-2 C-Band ciruclar polarization ratio (CPR) image over study area. The purple box surrounds anomalous radar rough area. The red circle outlines a large salt diapir for comparison.
That is super rough! How odd! But it definitely isn't salt, because the area doesn't show an anhydrite/gypsum signature in the spectral images:

Spectral (ASTER TIR) band composition of study site. Boxes are in same features as above image. Salt appears as dark maroon.  The mysterious radar-rough feature appears as dark blue.
Curiouser and curiouser! The rough area is appearing blue in the spectral image.  I'm not sure what that corresponds with in this band ratio - something to look up perhaps. However, we can definitely say it isn't salt.  Now, I know there are volcanic intrusions in the area, particularly in the Isachsen formation, so one of my ideas is that it could be made of lava. Lava is radar-rough.

I pulled up Harrison and Jackson's (2014) geological map of the site.  The area is mapped as Isachsen formation! At first I thought that confirmed my hypothesis that the area is lava, but then I looked at the detailed geological description of the units.  Whereas other Isachsen areas are mapped as basalt flows, or sedimentary units with localized volcanics, this area is just mapped as being limestone and siltstone.  No lava.  That is weird, because limestone shouldn't be producing a really rough signature. 

If we have time on one of our helicopter days in the field this July, I'd like to check it out!

RADARSAT-2 Data and Products (c) MacDonald, Dettwiler and Associates, Ltd. (2016) - All Rights Reserved. RADARSAT is an official trademark of the Canadian Space Agency.

Tuesday, May 16, 2017

Incised meanders - When uplift beats migration

Hello!

There has been a two-week hiatus in posts because I was at fieldschool! The Centre for Planetary Science and Exploration at Western hosts an annual/semi-annual planetary surface processes fieldschool in the southwest United States. As mentioned last post, we visited numerous sites in Arizona and Utah, where there are abundant geological and geomorphological features that shape the landscape. We tweeted extensively about the experience, and you can follow our updates and see many exciting pictures on the hashtag #PS9605.

One of my favourite sites that we visited might surprise you.  Even though we visited many famous sites like the Grand Canyon and Meteor Crater, I really appreciated Goosenecks State Park, Utah. I suppose my fluvial sedimentological side is showing!

To explain why I found this river channel so exciting, let's recall how meandering rivers form. There are four main types of river:
  1. Straight
  2. Anastamosing
  3. Braided
  4. Meandering
The shapes of these rivers are controlled by the slope gradient and types of materials being carried by the river. In general, the steeper the slope, the quicker the river moves and the larger sediments and grains it can carry. Meandering rivers are found in areas with the lowest slope gradient, and typically carry very fine grained sands and clays. 
Types of rivers (from University of Indiana course webpage)
Water flows turbulently in river channels, and the water undergoes what we call "helical flow", that is the water is being driven in a corkscrew-like motion as it travels downsteam. Imagine the forces acting upon water in a river: water at the bottom and at the sides of the channel are slowed down by drag forces against the channel walls. Water in the middle and top of the stream is free to move more quickly. We also know that an object in motion likes to stay in motion. This means that the water at the top of the river channel has more momentum when it collides with a bend in the river.  The water gets forced down the wall, and any sediments it is carrying will erode into what we call the "cutbank" on the meander loop. That water is then forced across the bottom of the channel, losing momentum from the drag forces, and slows enough to begin depositing sediments on the other side (the "point bar"). This cycle repeats, and we get meandering rivers as the cutbank is cut away and the point bars build up.  Meandering rivers migrate - if they keep cutting away and building point bars eventually the channels will move back and forth across the landscape. Sometimes rivers will even cut themselves off, trapping ponded water called "oxbow lakes". 
Depiction of helical flow in a meandering river, note how water is
being driven down the cutback, across the bottom of the channel
and then up the point bar (via The British Geographer, source unknown)
It isn't easy to visualize that process in words, so here is an animated gif to illustrate the evolution of meandering rivers:
Source: The skeptical geologist at this blog

Let's bring this back to Goosenecks State Park, where the San Juan River has incised into 300 m of limestone, siltstone, sandstone and shale cliffs.

Just look at this landscape.


180° panorama of Goosenecks State Park (Elise Harrington 2017)

At first glance, you go, "Wow, yup, that is a meandering river!" because it shows very dramatic sinuousity.

But once you start remembering how the meander process works, a sneaking suspicion will creep up on you... It didn't migrate. There is no floodplain, here! Look at the above gif - we know that these types rivers move around through time and cut themselves off. Here, the river somehow stayed in one place for long enough to eroded and incise downwards rather than laterally.

The reason?  The same as why the Grand Canyon is so deep! Within the past 6 million years, the Colorado Plateau has undergone significant tectonic uplift.  Uplift dramatically exacerbates erosion. Imagine pushing down on an object. Now imagine that as you are pushing down, it is pushing back up at you! You intuitively know that the force you feel is stronger, and this helps rivers cut down into canyons like the Goosenecks and the Grand Canyon far more quickly than they otherwise would be able. Because the river is incising so deeply, so quickly (on a geological time scale, of course) it is not able to migrate and meander, and becomes "locked" and only able to cut down vertically.

Standing at the edge of the cliffs was spectacular.  My brain had a difficult time processing the scale of the river, and how deep the canyons were.  I highly recommend checking it out if you are in southern Utah!