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Author Topic: Sentinel-1 C-band data over Arctic sea ice starting to be available  (Read 8389 times)

nukefix

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The operations and data provision are being ramped up. At the moment there are many SAR images over the arctic sea ice available on the data portal for science:

https://scihub.esa.int/

..unfortunately the data is not currently being added as it has been acquired but this should be happening soon..

Free toolbox for data handling is available here:

https://earth.esa.int/web/sentinel-tbx/sentinel-1-toolbox
« Last Edit: October 20, 2014, 06:51:09 PM by nukefix »

nukefix

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Re: Sentinel-1 C-band data over Arctic sea ice starting to be available
« Reply #1 on: October 20, 2014, 06:55:28 PM »
Here's the planned coverage for the next cycle, from https://sentinel.esa.int/web/sentinel/missions/sentinel-1/observation-scenario



ChrisReynolds

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Re: Sentinel-1 C-band data over Arctic sea ice starting to be available
« Reply #2 on: October 20, 2014, 07:44:57 PM »
Sentinel is a radar system, synthetic aperture by the looks of it.

Quote
The radar can distinguish between the thinner, more navigable first-year ice and the hazardous, much thicker multiyear ice to help assure safe year-round navigation in ice-covered Arctic and sub-Arctic zones. These radar images are particularly suited to generating high-resolution ice charts, monitoring icebergs and forecasting ice conditions.

http://www.esa.int/Our_Activities/Observing_the_Earth/Copernicus/Sentinel-1/Oceans_and_ice

One page there mentions tracking shipping, so the resolution should be very high.

Also reference to wave height, that suggests at least locally high vertical resolution. But does this mean that it will be able to monitor sea ice free board, that could open a new system for measuring volume. But locally high vertical resolution (wave peaks vs the sea level in the same shot), may not necessarily mean swathe resolution to measure freeboard of sea ice.

Yes it is synthetic aperture:
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Sentinel-1 carries a 12 m-long advanced synthetic aperture radar (SAR), working in C-band.

C band is around 7GHz, wavelength around 4cm. So wavelength won't be the limit to ground resolution.

Two modes.
Quote
Interferometric Wide swath mode, the default mode over land, has a swath width of 250 km and a ground resolution of 5 x 20 m. This mode images in three sub-swaths using the Terrain Observation with Progressive Scans SAR – or TOPSAR. With this technique, the radar beam scans back and forth three times within a single swath (called sub-swaths), resulting in a higher quality and homogeneous image throughout the swath.

Wave mode acquisitions – which can help to determine the direction, wavelength and heights of waves on the open oceans – are 20 x 20 km, acquired alternately on two different incidence angles every 100 km.
http://www.esa.int/Our_Activities/Observing_the_Earth/Copernicus/Sentinel-1/Radar_vision

Starting to sound very much like ASCAT, but I think ASCAT has a resolution of 30km. Sentinel seems to be slightly finer resolution. If it is like ASCAT it will be determining first year and multi year sea ice by the difference in dielectric constant between old and young ice and the impact on backscatter from the ice surface, not from freeboard.

However despite the time lag between passes Sentinel in interferometric wide swath mode might be able to measure freeboard if analysed by the right scientists - I'm not sure on that.

Thanks Nukefix. Might come in useful.

nukefix

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Re: Sentinel-1 C-band data over Arctic sea ice starting to be available
« Reply #3 on: October 21, 2014, 10:19:27 AM »

One page there mentions tracking shipping, so the resolution should be very high.
Over the Arctic the main modes are EW (50m resolution) and IW (20m resolution)

https://sentinel.esa.int/documents/247904/685163/Sentinel-1_User_Handbook

Quote
Also reference to wave height, that suggests at least locally high vertical resolution. But does this mean that it will be able to monitor sea ice free board, that could open a new system for measuring volume. But locally high vertical resolution (wave peaks vs the sea level in the same shot), may not necessarily mean swathe resolution to measure freeboard of sea ice.
Imaging the freeboard is not possible as it would require centimetric resolution to see the radar-shadow that the freeboard would cast. Wave-height is measured at a low resolution (kilometres) by a different method (via the change in the wave-pattern that happens during the imaging).

Yes it is synthetic aperture:
Quote
C band is around 7GHz, wavelength around 4cm. So wavelength won't be the limit to ground resolution.
Wavelength is 5.4cm to be exact.

Quote
Starting to sound very much like ASCAT, but I think ASCAT has a resolution of 30km. Sentinel seems to be slightly finer resolution.
The resolution is higher by a factor of 1000. ASCAT is a scatterometer which is a primitive type of radar, while SAR is rather advanced, hence the higher resolution.

Quote
If it is like ASCAT it will be determining first year and multi year sea ice by the difference in dielectric constant between old and young ice and the impact on backscatter from the ice surface, not from freeboard.
C-band SAR has been used in operational sea-ice monitoring for a long time.

Quote
However despite the time lag between passes Sentinel in interferometric wide swath mode might be able to measure freeboard if analysed by the right scientists - I'm not sure on that.
I don't think that will work, but S-1 will certainly provide daily imagery of sea ice in medium-high resolution for 20+ years into the future.

ChrisReynolds

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Re: Sentinel-1 C-band data over Arctic sea ice starting to be available
« Reply #4 on: October 21, 2014, 07:35:45 PM »
Thanks for the further detail, it filled the gaps I didn't have time to fill.
EDIT - ...and corrected some of my half-assed guesses.  :-[   ;)
« Last Edit: October 22, 2014, 06:48:03 PM by ChrisReynolds »

Wipneus

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Re: Sentinel-1 C-band data over Arctic sea ice starting to be available
« Reply #5 on: October 22, 2014, 11:40:34 AM »
Thanks nukefix, it reminded me to have a look at what is available.

A sample image is in the "Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland" thread.

MikeAinOz

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Re: Sentinel-1 C-band data over Arctic sea ice starting to be available
« Reply #6 on: January 11, 2015, 05:59:54 AM »
Thanks nukefix, I'd been looking at the Greenland/Kennedy area images and wondering how Sentinel worked. The user guide answers all those questions I had and more  :)
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Re: Sentinel-1 C-band data over Arctic sea ice starting to be available
« Reply #7 on: February 16, 2015, 02:36:42 AM »
So, we have some ice (that much is clear):



I'm guessing there isn't actually that much more open water/thin ice in the south of this chart, but that the darker south is due to the physical satellite flying from north to south. What's with the super–highways? Who or what constructed them and how are they able to survive all the storms and the general chaos of the Arctic sea? Where would you go to find open water?
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Gray-Wolf

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Re: Sentinel-1 C-band data over Arctic sea ice starting to be available
« Reply #8 on: February 16, 2015, 11:16:23 AM »
Hi Vids!

I'd imagine those 'super highways' work just the same as faulting in rocks? Any stresses and strains exploit the weakness and leave the rest of the ice intact ( or maybe act like a 'conservative plate margin' like the san andreas?).
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andy_t_roo

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Re: Sentinel-1 C-band data over Arctic sea ice starting to be available
« Reply #9 on: February 16, 2015, 11:30:02 AM »
re: resolution:

in multi-look, ground range measuring mode, IW resolution is 88x87 m, but the processed images are provied at 40x40m - the website has a fair bit of info on the different datasets available. https://sentinel.esa.int/web/sentinel/user-guides/sentinel-1-sar/resolutions/level-1-ground-range-detected

Jim Hunt

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Re: Sentinel-1 C-band data over Arctic sea ice starting to be available
« Reply #10 on: February 16, 2015, 02:05:23 PM »
I guess it should also be mentioned in here that Sentinel-1A GeoTIFFs and JPGs are also readily avaiiable from

http://www.polarview.aq/arctic

and a similar Antarctic URL. Here's the Larsen C "crack":

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johnm33

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Re: Sentinel-1 C-band data over Arctic sea ice starting to be available
« Reply #11 on: February 16, 2015, 02:53:32 PM »
Vid my wag on the highways is 'tidal' swells travelling in the same direction at different speeds cause long cracks where the peaks coincide the two sides then crash back together compacting the ice when the peaks have passed.

viddaloo

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Re: Sentinel-1 C-band data over Arctic sea ice starting to be available
« Reply #12 on: February 16, 2015, 05:11:15 PM »
Hi Vids!

I'd imagine those 'super highways' work just the same as faulting in rocks? Any stresses and strains exploit the weakness and leave the rest of the ice intact ( or maybe act like a 'conservative plate margin' like the san andreas?).

Hiya, Gråbein!

Let's just say I have friends who'd go down those roads any day. Even more so when there's absolutely no legend available to explain what we see in these icecharts. Do you want me to tell you a fat story? I can do that, but it will be fictional. Does anyone feel like making a [chart] legend or telling me what's in this plot? Not so much.

PS: I do understand professional oceanographers are the primary end–users of these charts. I still think they should come with a simple legend so simple people could understand. Neither ESA, DMI nor Polarview provide such a legend. And Google I believe requires search terms to be of help? It's not like you'll find the user manual coincidentally on the Google start page!
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viddaloo

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Re: Sentinel-1 C-band data over Arctic sea ice starting to be available
« Reply #13 on: February 17, 2015, 06:52:59 AM »
I have to add that the Polar View site and the Sentinel charts are super–cool. My only issue is the lack of an adequate legend or simple explanation of what you see in the charts, in areas where it isn't obvious — like the Nares Strait, which is a walk in the park compared to the areas around the Pole. In Nares, I guess the only question you have is what's water and what's thin ice.

I'll get around to meditating for hours over a North Pole area high–res Sentinel towards the end of the week, we'll see what comes out of it (either deep understanding or sensational sci–fi!).
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Pmt111500

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Re: Sentinel-1 C-band data over Arctic sea ice starting to be available
« Reply #14 on: February 17, 2015, 07:38:43 AM »
those highways are to my knowledge ridges of uneven ice and their apparent whiteness is a result of two sensor beams hitting them at slightly different angle resulting in a double exposure. could be wrong though. they're awfully long features not seen in the Baltic during normal winters, when the wider open seas do not freeze. similarly the crack in larsen C is nearly black since only one swath in sensor gets partial echo...
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viddaloo

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Re: Sentinel-1 C-band data over Arctic sea ice starting to be available
« Reply #15 on: February 17, 2015, 08:03:53 AM »
Awfully long, yeah! From what I understand they're like the Oslo to Trelleborg E6 motorway in length. That is southern Norway to extreme south Sweden, for the uninitiated. Trelleborg is where the Trelleborg–Saßnitz ferry departs to continental Europe (communist DDR in my youth).

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gurusan

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Re: Sentinel-1 C-band data over Arctic sea ice starting to be available
« Reply #16 on: May 28, 2015, 09:27:44 PM »
On a different topic: I know that Sentinel-1 has been providing operational data for a couple of months only. Having said that, are there any research papers, journal articles, or pre-prints available on the use of Sentinel SAR data for sea ice research till date?