Support the Arctic Sea Ice Forum and Blog

Author Topic: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland  (Read 807997 times)

A-Team

  • Nilas ice
  • Posts: 2454
    • View Profile
  • Liked: 305
  • Likes Given: 22
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1600 on: June 15, 2016, 05:34:32 PM »
At some point, the anomalous melt temperatures should lead to anomalous velocities. Wipneus provided a couple more S2A images which, though cloudy, might barely enable velocity measurement down the final straightaway.

S2A_R068_V20160611T151937.22WEB.B04.tiff
S2A_R111_V20160614T152913.22WEB.B04.tiff

The attached image shows a hypothetical research ice camp situated on one of the massive bergs pictured above. While the risk of over-turning or splitting are negligible a few days after calving, there is still an issue with tsunamis from new calving front events swamping the camp. For that reason tents (and researchers) are depicted tethered to an idling helicopter.

TenneyNaumer

  • New ice
  • Posts: 75
    • View Profile
    • Climate Change: The Next Generation
  • Liked: 1
  • Likes Given: 10
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1601 on: June 16, 2016, 04:41:52 AM »
Somebody please tell me there is something wrong with this image
http://ocean.dmi.dk/arctic/images/MODIS/Disko/20160615s01a.ASAR.jpg

nukefix

  • Frazil ice
  • Posts: 461
    • View Profile
  • Liked: 9
  • Likes Given: 1
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1602 on: June 16, 2016, 09:35:48 AM »
Somebody please tell me there is something wrong with this image
http://ocean.dmi.dk/arctic/images/MODIS/Disko/20160615s01a.ASAR.jpg
I see what you mean. That's an illusion though, a higher resolution S-1A image shows that there's a layer of floating debris in front of the real calving front that creates the illusion:

http://www.polarview.aq/images/105_S1jpgfull/S1A_IW_GRDH_1SSH_20160614T204645_BFBE_N_1.final.jpg

johnm33

  • Nilas ice
  • Posts: 1295
    • View Profile
  • Liked: 88
  • Likes Given: 43
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1603 on: June 16, 2016, 10:56:34 AM »
"Somebody please"
The tides are low, http://www.tide-forecast.com/locations/Egedesminde-Greenland/tides/latest [closest visual rep.] http://www.dmi.dk/fileadmin/user_upload/vandstand_txt_pdf/2016/Ilulissat2016.pdf [pdf] the ice is stuck, http://www.lookr.com/lookout/1310041325-Ilulissat
Wipneus, if you have the time and it's not too cloudy can you show us this area in daylight, it's the same area previously mentioned by Nukefix.

Wipneus

  • Citizen scientist
  • Young ice
  • Posts: 4009
    • View Profile
    • Arctische Pinguin
  • Liked: 644
  • Likes Given: 0
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1604 on: June 16, 2016, 05:17:46 PM »

Wipneus, if you have the time and it's not too cloudy can you show us this area in daylight, it's the same area previously mentioned by Nukefix.


Last one is 5 June. Later ones are all cloudy there.


A-Team

  • Nilas ice
  • Posts: 2454
    • View Profile
  • Liked: 305
  • Likes Given: 22
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1605 on: June 16, 2016, 07:22:41 PM »
Ouch ... nice of polar view to offer S1A but that file is truly too huge to be practical for a web browser (though Opera eventually got it). The image is showing more of the this year's somewhat  odd fjord melange freeze-up being pushed out of the south channel bay by active calving.

Note the calving front is not its usual arcuate self but rather has built up quite a bit of material in the NE corner. In the past, any departure from a smooth bow is soon restored by a calving event (though here little has changed since the June 5th Landsat, see #1593), which would involve a lot of material in this instance. Cracks can already be seen. The position of the calving front is not remarkable for mid-June.

The Landsat of 13-JUN-16 (LC80100112016165LGN00) is clear enough; that of 15-JUN-16 (LC80080112016167LGN00) is quite marginal. For analysis of the NE corner feature, the resolution of S2A would be preferable.
« Last Edit: June 17, 2016, 06:46:26 AM by A-Team »

johnm33

  • Nilas ice
  • Posts: 1295
    • View Profile
  • Liked: 88
  • Likes Given: 43
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1606 on: June 17, 2016, 12:26:16 AM »
Thanx Guv'nor whatever I thought I was seeing on sentinel, there's no sign of it in daylight.

Wipneus

  • Citizen scientist
  • Young ice
  • Posts: 4009
    • View Profile
    • Arctische Pinguin
  • Liked: 644
  • Likes Given: 0
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1607 on: June 17, 2016, 09:27:00 AM »
2016/6/15 ( R125) is in. This does not cover the calving fronts and the upstream parts of the ice stream are clouded.
What is visible is a striking swelling up of many melt ponds with associated water streams in a short time. The animation is a melt pond in the center of the thumb nail (first image).
The animation is scaled to 20m/pix, dates are 4 days apart.

Shared Humanity

  • Young ice
  • Posts: 3981
    • View Profile
  • Liked: 430
  • Likes Given: 52
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1608 on: June 18, 2016, 12:19:27 AM »
In the animation, it is fascinating to see what appears to be an already existing moulin from previous melt seasons appear as the main pond transforms into open water. The deep blue portion appears to be deep water as compared to the shallower edges. Is that what I am seeing?

oren

  • Young ice
  • Posts: 4537
    • View Profile
  • Liked: 916
  • Likes Given: 1307
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1609 on: June 18, 2016, 12:41:22 AM »
In the animation, it is fascinating to see what appears to be an already existing moulin from previous melt seasons appear as the main pond transforms into open water. The deep blue portion appears to be deep water as compared to the shallower edges. Is that what I am seeing?

I believe it is. Many melt lakes appear at the same location every year (which is still quite amazing to my layman mind).

plinius

  • Frazil ice
  • Posts: 403
    • View Profile
  • Liked: 0
  • Likes Given: 0
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1610 on: June 18, 2016, 02:37:19 AM »
The melt lakes carve holes/deeper parts into the ice surface, which are too strong for the next winter to even out. Similarly, the rivers eat pretty deeply into the ice (just calculate how much the flow actually warms the water and then melts the ice in their beds), so that you forcibly return to the old patterns... I don't think it should be too surprising (btw. the lakes are not in identical positions, they shift with the ice surface).

A-Team

  • Nilas ice
  • Posts: 2454
    • View Profile
  • Liked: 305
  • Likes Given: 22
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1611 on: June 18, 2016, 03:26:42 PM »
Quote
btw. the lakes are not in identical positions, they shift with the ice surface
It seems like lakes should move downhill to the west as carried along by ice sheet motion (whose speed and direction vary with location) but many of them don't. They've been sitting on the same spot for decades because water fills a depression reflecting a standing wave over a bedrock feature or a low pressure flow eddy at confluences of ice streams.

However, the firn and ice affected by where the melt lake was, do move as expected, just not the liquid location.

Locational stability is particularly noticeable for melt features in or adjacent to the main channel of Jakobshavn ice stream where the displacements should be extreme (up to 17 km/yr) and indeed trackable even day to day at S2A resolution but haven't been displaced in the recent satellite record.

An effect here could come from the annual vertical lowering trend of the surface which might change the dynamics creating the depression. This could even cause the melt feature location to migrate uphill.

Overall, the western Greenland ice sheet is very flat with a gradient of ~ 1% which is small relative to sastrugi, standing waves, and other irregularities which can vary year to year. This means melt water hardly knows which way to flow; indeed on the much-studied Lincoln glacier just to the south some of the melt streams do not follow the surface gradient. Thus you cannot predict flow channels merely from high precision lidar elevation mapping.

No stable surface drainage pattern of significant extent has become established on the west central Greenland ice sheet. There are no surface streams discharging into the sea or onto exposed coastal rock margin (though some emerge there from under the ice sheet). The water either refreezes where it melted or makes it way to bedrock or relocates somewhere in between as frozen lens or rarely as sub-surface lake.



The cumulative melt day graphic below for west-central and interior Greenland does not seem extraordinary even for Nuuk -- yet what is needed here is an anomaly display. The near-interior melt east and just south of the Jakobshavn calving front may be noteworthy.

If someone here is up to it, the data needed to make an anomaly display is stored as the MEaSUREs Greenland Surface Melt Daily 25km EASE-Grid 2.0 data set. It is based on SSMIS passive microwave data, the Near-Real-Time DMSP SSM/I-SSMIS Daily Polar Gridded Brightness Temperatures.

http://nsidc.org/greenland-today/about-the-data/
http://nsidc.org/data/nsidc-0533
« Last Edit: June 18, 2016, 04:02:20 PM by A-Team »

Wipneus

  • Citizen scientist
  • Young ice
  • Posts: 4009
    • View Profile
    • Arctische Pinguin
  • Liked: 644
  • Likes Given: 0
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1612 on: June 19, 2016, 08:41:25 AM »
2016/6/18 ( R025) is in. Cloud cover 60% but most features are visible through the rather thin clouds.
I have uploaded S2A_R025_V20160618T150914.22WEB.B04.tiff .
« Last Edit: June 19, 2016, 09:55:23 AM by Wipneus »

A-Team

  • Nilas ice
  • Posts: 2454
    • View Profile
  • Liked: 305
  • Likes Given: 22
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1613 on: June 19, 2016, 04:36:28 PM »
No drama at the calving front and none imminent. It appears that about half of the bergs are discharged from the north side. That does not mean half the volume (as we see only the surface and not freeboard) as they don't have the depth of the bergs from the main channel. The north side is responding to removal of buttressing as the main calving front retreats.

Things are going well at the imaginary berg ice camp which has floated stably (as expected) about halfway down the fjord. Researchers are enjoying a leisurely breakfast before resuming the trench cut (dotted lines show remaining work to do). This corresponds to drilling a core because the glacier slab is on its side. The helicopter (not shown) is ferrying samples back to a freezer in Illulisat.

The surface mass balance map shows a notable loss in the interior basin of Jakobshavn between the end of last season and mid-June.
« Last Edit: June 19, 2016, 05:27:20 PM by A-Team »

iwantatr8

  • New ice
  • Posts: 63
    • View Profile
  • Liked: 16
  • Likes Given: 4
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1614 on: June 22, 2016, 07:53:24 AM »
No drama at the calving front and none imminent. It appears that about half of the bergs are discharged from the north side. That does not mean half the volume (as we see only the surface and not freeboard) as they don't have the depth of the bergs from the main channel. The north side is responding to removal of buttressing as the main calving front retreats.


I hate to say this A-Team but it appears that there is some drama going on, looks like something happened yesterday given the changes in calving face and the Fjord.
 https://worldview.earthdata.nasa.gov/?p=arctic&l=MODIS_Terra_CorrectedReflectance_Bands721,MODIS_Terra_CorrectedReflectance_TrueColor,Coastlines&t=2016-06-21&v=-312303.6758297126,-2350251.7529409253,-66543.67582971259,-2219819.7529409253

Landsat seems to have (amazingly,given coverage this year so far) a pretty clear view of things.
http://earthexplorer.usgs.gov/browse/landsat_8/2016/082/233/LC80822332016174LGN00.jpg

Laurent

  • Young ice
  • Posts: 2536
    • View Profile
  • Liked: 6
  • Likes Given: 24
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1615 on: June 22, 2016, 09:20:57 AM »
Yes certainly an other big calving event. Have we reach the point where the melting goes on the other side of the slope, because on this side there seems to be only one exit and it is Jakobshavn Isbrae.

Wipneus

  • Citizen scientist
  • Young ice
  • Posts: 4009
    • View Profile
    • Arctische Pinguin
  • Liked: 644
  • Likes Given: 0
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1616 on: June 22, 2016, 10:32:02 AM »
Also a clear Sentinel image from 2016/6/21 ( R068 ). Uploaded  S2A_R068_V20160621T151912.22WEB.B04.tiff

« Last Edit: June 22, 2016, 11:42:02 AM by Wipneus »

swoozle

  • New ice
  • Posts: 23
    • View Profile
  • Liked: 3
  • Likes Given: 17
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1617 on: June 22, 2016, 10:47:09 AM »
Hopefully I'm not the only noob that has scoured those shots and can't see the change; can one of you guys point at exactly where this event occurred? Thanks!

Adam Ash

  • Frazil ice
  • Posts: 306
    • View Profile
    • The 100 metre line
  • Liked: 8
  • Likes Given: 20
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1618 on: June 22, 2016, 11:59:47 AM »
This report on the Antarctic pages shows the impact of melt ponds on internal ice temperature and structure...

http://forum.arctic-sea-ice.net/index.php/topic,322.msg80331.html#msg80331

Similar things will no doubt be happening under all those pretty blue ponds in Greenland.  This would seem to confirm the heat transport role of the melt ponds.


Laurent

  • Young ice
  • Posts: 2536
    • View Profile
  • Liked: 6
  • Likes Given: 24
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1619 on: June 22, 2016, 12:17:41 PM »
swoozle : You can see the retreat line of the glacier in red, in front of the glacier there is a zone (grey)  that is filled with new ice. When the ice decay the bottom of the iceberg is topped over and the colour of old ice is blue. Does it help ?
http://go.nasa.gov/28N4Dbu
« Last Edit: June 22, 2016, 12:33:42 PM by Laurent »

swoozle

  • New ice
  • Posts: 23
    • View Profile
  • Liked: 3
  • Likes Given: 17
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1620 on: June 22, 2016, 02:34:28 PM »
swoozle : You can see the retreat line of the glacier in red, in front of the glacier there is a zone (grey)  that is filled with new ice. When the ice decay the bottom of the iceberg is topped over and the colour of old ice is blue. Does it help ?
http://go.nasa.gov/28N4Dbu

Yes, thanks very much!

A-Team

  • Nilas ice
  • Posts: 2454
    • View Profile
  • Liked: 305
  • Likes Given: 22
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1621 on: June 23, 2016, 01:23:42 AM »
Folks, don't waste your time on compressed low resolution imagery taken with 1999 satellite technology when we have a billion dollar 2015 instrument providing free 10m scenes that can be processed down to 5m on clear days.
 
Wipneus has taken all the sting out of alert tracking, processing to a common file format, and posting to a very fast and convenient source for download. Yet how many people are posting away without utilizing the resource?

You just cannot stay in the game looking at Jakobshavn with Modis or DMI on a cell phone; there is nothing further anyone here can do to help if that is your only device (no bandwidth, no storage no image processing capacity).

As mentioned many times, Jakobshavn calves continuously throughout the year. If the front of the ice stream is moving westward at 50 meters per day yet the calving front appears stationary, that's because a volume of 50 m length x 5 km width x 1200 m depth is falling into the fjord bay each day.

We are primarily on the look-out for (1) record retreat that removes side buttressing, thus accelerating further retreat and (2) a repeat of monstrous calving cascade of 15 Aug 15 which could be indicative of unanticipated (by models) internal mechanical ice failure, especially if we see it again in 2016.

Below are 5 m scenes from the 18th, 21st and 22nd of June 2016. The hazy 18th we've seen a portion of earlier; the S2A of the 21st is an extraordinary image with a curious feature; the followup Landsat of the 2nd is an ascending orbit oblique seasonal low sun angle not up to Sentinel quality when enlarged to 5 m.

What's odd about the calving front (middle image below) is that the shape of the newly calved berg almost seems to fit the bite in the calving front. However the bite hasn't gone nearly through to the bottom of the calving front ice. It's almost as though a horizontal section has flaked off.

If, more likely, the bite is just ordinary floating calved ice that just hasn't made its way clear of the front and is not related to the larger berg, that too is worth following because the calving front usually maintains its arcuate shape and doesn't form stable bites.

« Last Edit: June 23, 2016, 01:37:20 AM by A-Team »

sidd

  • Young ice
  • Posts: 4987
    • View Profile
  • Liked: 389
  • Likes Given: 0
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1622 on: June 23, 2016, 05:25:54 AM »
" If ... the bite is just ordinary floating calved ice ..."

Yes. If there was water under that section, that is significant.

nukefix

  • Frazil ice
  • Posts: 461
    • View Profile
  • Liked: 9
  • Likes Given: 1
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1623 on: June 23, 2016, 09:55:39 AM »
And for the radar POV, here's S-1A on 14.6, 1st snapshot is 10m UTM22 as usual and the second one is an overview shot showing what is happening further up the ice sheet...wet snow is a great absorber and shows up very dark..


Laurent

  • Young ice
  • Posts: 2536
    • View Profile
  • Liked: 6
  • Likes Given: 24
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1624 on: June 23, 2016, 09:56:04 AM »
A-Team : You mean worldview isn't good enough. We have better like what ? http://www.polarview.aq/arctic ? I see a B/W (beurk ;)) Is there something easy to catch the satellite pictures with good resolution ?

Tealight

  • Frazil ice
  • Posts: 431
    • View Profile
    • CryosphereComputing
  • Liked: 133
  • Likes Given: 14
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1625 on: June 23, 2016, 08:55:48 PM »
Is there something easy to catch the satellite pictures with good resolution ?
Amazon Web Services for Sentinel 2 and Earth Explorer for Landsat.

For Jakobshavn I have bookmarked the correct tile and check for new images a few times a week:
http://sentinel-s2-l1c.s3-website.eu-central-1.amazonaws.com/#tiles/22/W/EB/2016/

The jp2 format on Amazon is great for small download sizes and saving diskspace, but terrible for image processing. I use Esa's SNAP application to convert it to ENVI format and then work with different Bands at the same time. Wipneus and A-Team on the other hand use ImageJ or ImageMagick and tiff image format.
What I like about SNAP is the inbuilt geographic reference system and easy calculation of RGB images from different bands. Unlike A-Team I prefer posting images in RGB, because humans evolved with colour vision and can extract much more information from the same image by combining three different wavelengths.

At the same time I have to mention that viewing a 10980x10980 pixel image in full quality is a completly different experience than seeing a small crop with jpeg compression losses here on the forum. Sometimes I download S2A images just to go sightseeing in the arctic. The quality is comparable to looking out of an airplane window a few thousand feet above ground.

Attached is an image showing new ice free areas near the calving front, which might become a future place to set up a webcam. This a false colour image where the red band is replaced by near infrared to increase contrast. The ice is more blue and the rock is more red than in true colour.
« Last Edit: June 24, 2016, 12:36:34 AM by Tealight »

Laurent

  • Young ice
  • Posts: 2536
    • View Profile
  • Liked: 6
  • Likes Given: 24
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1626 on: June 23, 2016, 10:40:32 PM »
Thank you very much !
The information for the tiles is here :
http://sentinel-pds.s3-website.eu-central-1.amazonaws.com/

For ESA SNAP :
http://step.esa.int/main/download/
I don't know how to install it, but I will find...

Imagemagik : http://www.imagemagick.org/script/binary-releases.php
Available directly for Debian/Ubuntu users.

But I can't find the Tiff, do you know where they are ? Also Why there is so much file B01, b02... I have to download all of them ?

Tealight

  • Frazil ice
  • Posts: 431
    • View Profile
    • CryosphereComputing
  • Liked: 133
  • Likes Given: 14
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1627 on: June 24, 2016, 12:28:37 AM »
Tiff is just an image file format and not a program you can download. All other links are correct.

For a natural colour image you have to download B02,B03 and B04. B08 has the same 10m resolution for near inrared wavelength.
Maybe B12 is useful for thermal imaging like brightness temperature in Worldview.
https://en.wikipedia.org/wiki/Sentinel-2#Instruments

I personally don't use the Amazon tile information website anymore. Google Earth or a special Google Maps version give me the exact tile code and I don't have to adjust sliders for cloud cover or capture dates.

Military grid web version:
https://mappingsupport.com/p/coordinates-usng-google-maps.html

Military grid rid kmz file (Google Earth):
https://sentinels.copernicus.eu/documents/247904/1955685/S2A_OPER_GIP_TILPAR_MPC__20151209T095117_V20150622T000000_21000101T000000_B00.kml/ec05e22c-a2bc-4a13-9e84-02d5257b09a8
« Last Edit: June 24, 2016, 12:33:52 AM by Tealight »

Laurent

  • Young ice
  • Posts: 2536
    • View Profile
  • Liked: 6
  • Likes Given: 24
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1628 on: June 24, 2016, 11:36:35 AM »
I know tiff is a file format but .jp2 is a file format also, right ? so, what you are saying is we get the tiff through the .jp2 format that is already compressed ?

There is no coverage for the Arctic ? Is it due to the orbit of the satellites ?



Tealight

  • Frazil ice
  • Posts: 431
    • View Profile
    • CryosphereComputing
  • Liked: 133
  • Likes Given: 14
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1629 on: June 25, 2016, 01:03:03 AM »
Yeah we get the tiff format from jp2. I think the high compression of jp2 makes it hard to work with because the computer has to decompress the image. At least SNAP has problems with it. With just a few bands opened at the same time I managed to fill 32GB of RAM, high CPU load and make SNAP unresponsive. When I work with ENVI format 3-4GB of RAM are more then enough and every part of the band/image loads within a second.

Sentinel 2 has an inclination of 98.58 degrees, pretty typical for a Sun-synchronous satellite. This means latitudes above 84 degrees are not covered. (assuming 150 km swath width) Due to the enormus volume of data oceans are generally not captured.

You should defenitly read the Sentinel 2 user guide:
https://earth.esa.int/web/sentinel/user-guides/sentinel-2-msi/overview

Wipneus

  • Citizen scientist
  • Young ice
  • Posts: 4009
    • View Profile
    • Arctische Pinguin
  • Liked: 644
  • Likes Given: 0
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1630 on: June 25, 2016, 04:22:06 PM »
2016-06-24 (R111) is in. Clouds over some of the ice debris and floating ice bergs.
I uploaded S2A_R111_V20160624T152911.22WEB.B04.tiff 

Tealight

  • Frazil ice
  • Posts: 431
    • View Profile
    • CryosphereComputing
  • Liked: 133
  • Likes Given: 14
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1631 on: June 26, 2016, 11:24:16 PM »
Nothing interesting at the calving front, so I was playing around with GIMP.

The attached image is a size comparison between Manhatten and Jakobshavn at 10m resolution. The biggest ice bergs in the fjord are cropped and put on top of the base layer. The current calving front is indicated with a black line.

Click to see full resolution.

A-Team

  • Nilas ice
  • Posts: 2454
    • View Profile
  • Liked: 305
  • Likes Given: 22
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1632 on: June 28, 2016, 05:21:46 PM »
Below is the calving front on June 24th as supplied by wipneus at the gedeeld courtesy site http://tinyurl.com/jqo2lq7

It is rotated 42º in bicubic mode and optimized below for contrast while still in 16-bit tif format. If you start with an 8-bit download, obviously you are then stuck in 8-bit mode, so your software won't be able to do the necessary interpolations accurately and the product will be posterized (have a jumpy histogram not utilizing the full 256 gray options).

Be sure you understand contrast and bit depth before taking on 'true' color and false color (eg 367 or 721 Modis) which are vastly more complex to optimally process and interpret. We have 4 people out of 980 registrants who are color-capable at this point.

A lot of people posting here seem not to have read our earlier lengthy discussion of S2A images, their inconvenient jp2 (jpeg2000) format, the bit depth the satellite provides, and the open source software that can process them properly.

Please note that the forum offers a convenient and effective search for distinctive text words such as jp2 or jpeg2000 and google too allows the same search restricted to the forum domain.

The June 24th calving front has cured itself of its previous anomaly. The front has a normal curvature and retreat position for this date. It  needs a click to display properly.
« Last Edit: June 28, 2016, 05:26:50 PM by A-Team »

nukefix

  • Frazil ice
  • Posts: 461
    • View Profile
  • Liked: 9
  • Likes Given: 1
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1633 on: June 28, 2016, 05:25:12 PM »
Is it not possible to pre-process S-2 in 16bits with the ESA SNAP toolbox? It should be possible to make and share a graph that does all the necessary operations..

A-Team

  • Nilas ice
  • Posts: 2454
    • View Profile
  • Liked: 305
  • Likes Given: 22
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1634 on: June 28, 2016, 05:44:34 PM »
Quote
ESA SNAP toolbox? It should be possible to make and share a graph [describing an algorithm] that does all the necessary operations.
Apparently it drops to 8-bit while still requiring far too much RAM and processing time (see #1631 above) for 3-channel color. Note there seems to be no way of sharing 16-bit products through the forum -- upload a 16-bit png as image (or attachment) and it will display (and download) as 8-bit.

Attachments are restricted to gif, jpg, mpg, pdf, png, and txt. Tif is not supported even as 8-bit. Our monitors can only display three channels of 8-bit. Even a colorless grayscale is displayed that way, equal values of R,G, and B.

A graph could only take things so far. Each image requires manual contrast adjustment because of variable illumination, cloud cover, and region of interest (ROI). For example, optimizing to ice stream features (ie velocity tracking) sacrifices image quality of rocks without separate masking with an alpha channel prior to processing.

S2A is not dedicated or optimized to ice sheets by any means. One minute it is over Jakobshavn, the next over the Amazon. The ESA takes care of a whole lot of issues but necessarily leaves some to the end user.

The issue is, of the information initially gathered by the satellite's sensors, how much are you willing to throw away? Some of that information is explicit (readily visible) and some implicit (present, but has to be drawn out).

If all you want to do is monitor calving front position, you can do that with the crude Landsat or DMI preview images. There is no need to download anything, just take a screenshot in your web browser.

If you want to measure slight seasonal or year-on-year acceleration of the Jakobshavn Isbrae (ie is trouble brewing?), you need the full resolution of S2A and an optimal channel (which we previously determined was band 4; it gets into the shadows better). Color is great for melt but contributes adversely to matching displaced and distorted surface features.

Because the imagery is really expensive and enhancement is really cheap, it makes sense to intervene slightly between applications of successive algorithms. Here you'll get a sub-optimal outcome applying automatic pattern recognition to a sub-optimal image.

Does it matter? Yes because it is all about the error bars. We're trying to push out the best possible real-time prediction here; the uncertainty is an integral part of that.

The image below shows S2A_R111_V20160624T152911.22WEB.B04.tiff right out of the box. Note it is only using a fraction of the 16-bit range available to it. However dumbing it down to 8-bit makes matters considerably worse (histogram on right). Never round off your precision at the first step, save that until the very end.
« Last Edit: June 28, 2016, 07:00:14 PM by A-Team »

Espen

  • Young ice
  • Posts: 3251
    • View Profile
  • Liked: 177
  • Likes Given: 0
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1635 on: June 28, 2016, 08:21:25 PM »
Jakobshavn Isbræ is calving another (very) big calf:
« Last Edit: June 28, 2016, 08:34:58 PM by Espen »
Have a ice day!

Shared Humanity

  • Young ice
  • Posts: 3981
    • View Profile
  • Liked: 430
  • Likes Given: 52
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1636 on: June 28, 2016, 11:21:53 PM »
Wow.

iwantatr8

  • New ice
  • Posts: 63
    • View Profile
  • Liked: 16
  • Likes Given: 4
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1637 on: June 29, 2016, 08:28:41 AM »
Wow Indeed!

Fortunately the Sentinal 1A images are back at Polar View
http://www.polarview.aq/arctic

And a crop from yesterdays clear image gives us...

Wipneus

  • Citizen scientist
  • Young ice
  • Posts: 4009
    • View Profile
    • Arctische Pinguin
  • Liked: 644
  • Likes Given: 0
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1638 on: June 29, 2016, 08:57:18 AM »
Also visible on cloud free Sentinel 2A image from 2016/6/28 ( R025 ). I have uploaded S2A_R025_V20160628T150914.22WEB.B04.tiff .
« Last Edit: June 29, 2016, 10:39:30 AM by Wipneus »

nukefix

  • Frazil ice
  • Posts: 461
    • View Profile
  • Liked: 9
  • Likes Given: 1
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1639 on: June 29, 2016, 10:41:23 AM »
Quote
ESA SNAP toolbox? It should be possible to make and share a graph [describing an algorithm] that does all the necessary operations.
Apparently it drops to 8-bit while still requiring far too much RAM and processing time (see #1631 above) for 3-channel color.
Hmm, I haven't tried it personally but once the S2 product is opened (the .zip, not the .jp2 inside it directly) it can be saved into the internal BEAM-DIMAP format. In my experience SNAP deals well with RAM and huge images since it has a tiled memory management model (only the required tiles consume RAM, no need to put the whole product in there).

Darvince

  • Frazil ice
  • Posts: 287
    • View Profile
    • NSIDC Daily
  • Liked: 19
  • Likes Given: 6
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1640 on: June 29, 2016, 10:43:54 AM »
Also visible on cloud free Sentinel 2A image from 2016/6/28 ( R025 ). I have uploaded S2A_R025_V20160628T150914.22WEB.B04.tiff .

The most remarkable thing to me about the first image posted is the complete disappearance of some melt ponds on the ice sheet. Is that caused by refreezing or draining into the ice sheet?

oren

  • Young ice
  • Posts: 4537
    • View Profile
  • Liked: 916
  • Likes Given: 1307
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1641 on: June 29, 2016, 12:50:30 PM »
Wow! A big one, and on all fronts simultaneously.

nukefix

  • Frazil ice
  • Posts: 461
    • View Profile
  • Liked: 9
  • Likes Given: 1
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1642 on: June 29, 2016, 02:27:14 PM »
Isn't there an area a bit upward from the calving front where the glacier bed deepens again? I wonder when the calving-front moves over there and whether that change could be semi-permanent..

Shared Humanity

  • Young ice
  • Posts: 3981
    • View Profile
  • Liked: 430
  • Likes Given: 52
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1643 on: June 29, 2016, 03:58:33 PM »
I am sure this has been a persistent feature but my attention has been drawn to the dramatic drop in elevation of the main glacier stream at the point where it ends its western journey and begins to turn north. This can be clearly seen on this recently posted image.

It is obvious that, on the sides of the main stream, this is caused by the grounded ice finally finding its way to the main stream but what is the cause of the similar drop in elevation in the main ice flow at the point that it begins its turn north? Is it the underlying bed topography? Is it evidence of basal melt and outflow? Could it be driven by fjord water pushing back the grounding line?

johnm33

  • Nilas ice
  • Posts: 1295
    • View Profile
  • Liked: 88
  • Likes Given: 43
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1644 on: June 29, 2016, 05:09:30 PM »
 "drop in elevation" I had similar thoughts but there's no sign of it on the higher res. images, that said looking at this there is an underlying feature there.

I think this was originally posted by Sidd way up thread.

A-Team

  • Nilas ice
  • Posts: 2454
    • View Profile
  • Liked: 305
  • Likes Given: 22
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1645 on: June 29, 2016, 05:10:44 PM »
As Landsat awakens from its 5 hour slumber for system maintenance, it does not show further calving for the following day June 29th in LC80832332016181LGN00 at the blue shown in the first S2A 5m image. This is one of these odd late afternoon path,row that has very useful shadows.

Some other regions of interest are also colored: the purple for its striations, the yellow for its lag and odd eddy features, the green for imminent north side calving. It needs a click to display at its 5 m resolution. None of these have changed in the image of the 29th, though some of the larger bergs have fractured.

The north branch is also getting interesting -- quite a nice S2A scene on the 28th. Some new rocks may have become exposed on the west side.
« Last Edit: June 29, 2016, 05:37:49 PM by A-Team »

magnamentis

  • Guest
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1646 on: June 29, 2016, 05:22:11 PM »
I am sure this has been a persistent feature but my attention has been drawn to the dramatic drop in elevation of the main glacier stream at the point where it ends its western journey and begins to turn north.

as the melting and warming continues the ice is most probably getting thinner and therefore underlaying topographic features are starting to show, just imagine a riverbed that is 1 meter deep flowing over stones and other underwater irregularities and then the same riverbed with 5 meter water depth. in the latter case you will barely notice any turbulence if anything while in the first case you will have the typical "rapid" like flow.

oren

  • Young ice
  • Posts: 4537
    • View Profile
  • Liked: 916
  • Likes Given: 1307
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1647 on: June 29, 2016, 05:30:29 PM »
I am sure this has been a persistent feature but my attention has been drawn to the dramatic drop in elevation of the main glacier stream at the point where it ends its western journey and begins to turn north. This can be clearly seen on this recently posted image.

It is obvious that, on the sides of the main stream, this is caused by the grounded ice finally finding its way to the main stream but what is the cause of the similar drop in elevation in the main ice flow at the point that it begins its turn north? Is it the underlying bed topography? Is it evidence of basal melt and outflow? Could it be driven by fjord water pushing back the grounding line?

I believe this is an underlying topography thing. Note that almost half the width of JH after the bend doesn't come from the main stream but from the southwestern side of the bend. There were amazing animations in this thread from a few months ago of hi-res flows in this area, don't have time to find them now, they were extremely instructive.

Tealight

  • Frazil ice
  • Posts: 431
    • View Profile
    • CryosphereComputing
  • Liked: 133
  • Likes Given: 14
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1648 on: June 30, 2016, 11:10:26 PM »
Is it not possible to pre-process S-2 in 16bits with the ESA SNAP toolbox? It should be possible to make and share a graph that does all the necessary operations..

Quote
ESA SNAP toolbox? It should be possible to make and share a graph [describing an algorithm] that does all the necessary operations.
Apparently it drops to 8-bit while still requiring far too much RAM and processing time (see #1631 above) for 3-channel color.
Hmm, I haven't tried it personally but once the S2 product is opened (the .zip, not the .jp2 inside it directly) it can be saved into the internal BEAM-DIMAP format. In my experience SNAP deals well with RAM and huge images since it has a tiled memory management model (only the required tiles consume RAM, no need to put the whole product in there).

Converting a band to 16bit BEAM-DIMAP is no problem. Just select 'uint16' instead of 'uint8' under Raster/DataConversion/ConvertDatatype/Processing Parameters  and save the parameters as a graph. Then click 'batch processing', select your bands, load your graph and SNAP does the rest.

My problem with it is that all bands are still different products. It's enough to create an RGB image, but you can't read out individual pixel values for all bands at the same time.

To solve that I've written a python script which copies the image files to a new location (AWS.data) and assigns each band a proper name instead of band_1. A modified .dim file (BEAM-DIMAP format) then reads all bands together in one product.

 Edit: It is also possible to convert single bands to 16 bit geotiff.
« Last Edit: July 01, 2016, 01:06:13 AM by Tealight »

nukefix

  • Frazil ice
  • Posts: 461
    • View Profile
  • Liked: 9
  • Likes Given: 1
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1649 on: July 01, 2016, 11:02:41 AM »
My problem with it is that all bands are still different products. It's enough to create an RGB image, but you can't read out individual pixel values for all bands at the same time.
That should not be the case, at least it isn't with S-1 data and it's easy to do the same operation for all bands of an image, and have the output to be a single product.