[HN Gopher] Sky lapse in two tone
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Sky lapse in two tone
Author : ltrg
Score : 237 points
Date : 2024-03-07 10:48 UTC (12 hours ago)
(HTM) web link (blog.datadesk.eco)
(TXT) w3m dump (blog.datadesk.eco)
| hardlianotion wrote:
| I had no idea shipping lanes were so densely populated.
|
| EDIT - thanks all. I'll read it next time ...
| sokoloff wrote:
| Those are composite renders, integrating over time, not a
| snapshot.
|
| > Created in Google Earth Engine, these pictures are
| effectively annual timelapse images based on Sentinel-1's
| radar, consisting of multiple snapshots taken by the satellite
| across 2023.
| rob74 wrote:
| To quote the article:
|
| > _Inspired by some similar images shared by Tim Wallace in
| 2020, we've created a series of black-and-white composite
| renderings of some of the points of flux in the global energy
| system. Created in Google Earth Engine, these pictures are
| effectively annual timelapse images based on Sentinel-1's
| radar, consisting of multiple snapshots taken by the satellite
| across 2023._
|
| Not sure if the wind farm images are also composites (wouldn't
| make a lot of sense), but those of shipping lanes definitely
| are...
| d1sxeyes wrote:
| These are composites, although it's not clear exactly how many
| images are composed to build the final view.
| cricalix wrote:
| You can look at Marine Traffic to get a better sense of now
| versus the composites in the article.
| mysterypie wrote:
| Here's a site that does live tracking of ships:
|
| https://www.marinetraffic.com/en/ais/home/centerx:1.7/center...
|
| "Since December 2004, the International Maritime Organisation
| (IMO) requires all passenger and commercial vessels over 299
| Gross Tonnage that travel internationally to carry an AIS
| transponder that include a GPS receiver which collects the
| vessel's position and movement details."
|
| Counting across the longest segment of ships at the narrowest
| point of the English Channel in the feature article I see about
| 18 ships. In the live image from marinetraffic I see about 8.
| So even though the feature article is a composite image, the
| English Channel is indeed pretty crowded.
| hardlianotion wrote:
| Yes, you can still see the shipping lanes very clearly.
| buzzm wrote:
| Outstanding link; thanks for sharing.
| louthy wrote:
| The English channel is apparently busiest shipping lane in the
| world, so it's not surprising that it looks so busy on these
| images.
| jvanderbot wrote:
| Technical SAR question: Is the sea surface removed post-hoc, or
| does the sea not reflect these radar waves in a sufficient amount
| to show up? I seem to remember NISAR [1] will map land and ice -
| so presumably water ice shows up.
|
| I ask b/c if they are synthetically removing the sea surface at
| 1-5m resolution that seems _really hard_ given tides, waves, etc.
|
| 1. https://en.wikipedia.org/wiki/NISAR_(satellite)
| enriquto wrote:
| The liquid water absorbs most of the radar wave (at least for
| the C band, as is the case of sentinel-1). Thus, in the images
| it appears natively "black". When there are a lot of waves, the
| surface of the water forms some spurious reflectors that appear
| as a light texture in the surface, but the signal is definitely
| less powerful than metal/concrete reflectors of buildings and
| ships. Notice that in the "Humber" image of TFA you can
| appreciate some texture in the water. The contrast in this
| image has been exaggerated a lot, which saturates most of the
| land.
| m2fkxy wrote:
| It actually does not absorb radar energy, rather it reflects
| it away (specular reflection). That's why rougher sea surface
| appears brighter on SAR as it turns from a specular to a
| diffuse scatterer. Furthermore, in some specific conditions
| (low incidence angle, closer to nadir), calm water can appear
| much brighter than other land surfaces.
| enriquto wrote:
| thanks for the clarification! I'm just used to looking to
| the images without thinking too much about the water.
|
| I've never seen "close to nadir" radar images... wouldn't
| the ground fold over itself?
| m2fkxy wrote:
| Nadir-SAR would look very confusing, full of ambiguities,
| and probably unexploitable since the ranging part of
| RADAR would not be able to distinguish the left returns
| from the right returns -- that's why SAR is side-looking.
|
| even with a strictly side-looking geometry, images
| collected closer to nadir (steep/low incidence) start
| exhibiting some artifacts such as nadir returns [1].
|
| [1] https://www.researchgate.net/figure/Example-of-nadir-
| echo-in...
| m2fkxy wrote:
| Calm water surface is a specular scatterer, meaning radar
| energy will be reflected away, and proportionally so as the
| incidence angle increases.
|
| Images collected at lower incidence (closer to nadir) might
| feature very bright surface water if it is calm, as more energy
| is reflected towards the radar.
|
| Rough water surface is a diffuse scatterer, and will generally
| appear brighter than calm waters.
| fithisux wrote:
| Any good source for SAR image formation? From antennas to
| image processing?
| m2fkxy wrote:
| I am just a half-educated layman when it comes to SAR,
| which has a very heavy electrical engineering heritage. I
| hear that one very good technical resource is this book
| written by Iain Woodhouse [1], but I would be lucky to
| understand a tenth of it myself.
|
| There is also a very good SAR vulgarisation book written by
| Tom Ager [2].
|
| [1] https://www.routledge.com/Introduction-to-Microwave-
| Remote-S...
|
| [2] https://www.amazon.com/Essentials-SAR-Conceptual-
| Remarkable-...
| notahacker wrote:
| They're composite images, so there's definitely some post-
| processing going on. The sea surface will show up darker, but
| SAR is sufficiently sensitive to to detect oil slicks.
| sparsely wrote:
| I wonder at what density of wind farms they begin to interfere
| with each other's generating capacity. Presumably within one farm
| the turbines are sufficiently spaced that the reduction in power
| is minimal, but how large can an individual one get? Or is the
| amount of energy they take out of the wind negligable?
| gmane wrote:
| You pretty much answered your own question: compared to the
| size of the coast, the amount of energy these wind farms
| capture is negligible. You might see a reduction of power if
| you built a dense farm up and down an entire coast, but even
| then, the ocean is big compared to these farms.
|
| Edit to add: the Hornsea wind farm featured in this article is
| 2.5 GW and about 400 sq miles. [0]. The total energy capacity
| of existing generation assets is on the order of 7,500 GW [1].
| Let's double that, so 15,000 GW, which would be about 2,400,000
| sq miles. There's 1,015,756 linear miles of coast [2]. We know
| Hornsea is roughly square, so a 20 mile deep set of turbines
| doesn't interfere with each other, so that gives us ~20,000,000
| sq miles of usable coast for wind, and again, if we double the
| existing electrical generation for the earth, we'd cover
| 2,400,000 sq miles. (obviously not all of that is usable, but
| we're talking orders of magnitude here) There's really no
| conceivable situation where we'd build enough wind farms to
| interfere with each other.
|
| [0] https://en.wikipedia.org/wiki/Hornsea_Wind_Farm
|
| [1] https://www.statista.com/statistics/267358/world-
| installed-p...
|
| [2] https://en.wikipedia.org/wiki/Ocean
| DavidPeiffer wrote:
| I don't have the answer handy, but I do know there is a ton of
| research that goes into wind farm optimization. Location of the
| towers, cost to build, etc.
|
| I am curious how much small elevation differences impact
| optimal positioning of turbines, as that is a non-issue with
| offshore wind. The turbines in land-based wind farms are not in
| a nice grid like the offshore wind farm.
| https://openinframap.org/#9.68/41.6112/-92.4971
|
| The excerpt from an abstract below mentions the wake turbulence
| can cause other turbines to shut down.
|
| "...The distance between the turbines is among other things
| dependent on the recovery of wind energy behind the neighboring
| turbines and the increased wind load. Models for the mean wind
| speed and turbulence intensity in wind turbine parks are
| considered with emphasis on modeling the spatial correlation.
| Representative limit state equations for structural failure of
| wind turbine towers are formulated. The probability of failure
| is determined taking into account that wind turbines are parked
| for wind speeds larger than 25 m/s resulting in reduced wind
| loads. An illustrative example is presented where illustrative
| models for the spatial correlation is taken into account"
|
| https://www.tandfonline.com/doi/full/10.1080/102866006011566...
| The_Colonel wrote:
| Wikipedia has a short paragraph on the topic with some
| references for more details:
| https://en.wikipedia.org/wiki/Wind_farm#Turbine_spacing
| helsinkiandrew wrote:
| A maximum of 60% of the winds power can be extracted from wind
| (Bet'z law [1]) and modern turbines are only capable of
| catching 80% of that. There's lots of research in optimal
| spacing.
|
| I read that a rule of thumb was 4-5 diameter widths between
| turbines at right angles to prevailing wind and then 7 diameter
| widths between rows facing the wind
|
| [1] https://en.wikipedia.org/wiki/Betz%27s_law
| algo_trader wrote:
| Off topic: are there datasets for solar incidence over the oceans
| ?
|
| There are plenty of accurate maps/widgets for ground based PV,
| but ocean data seems much rarer
| Cthulhu_ wrote:
| That's because ocean PV is... unrealistic; the wear and tear on
| these things is immense. I am guessing windmills are affected
| less, with the blades being made out of fiberglass and most of
| the construction being above the waves.
|
| Source: I made it up, I'm a software engineer not a maritime
| power expert.
| jpm_sd wrote:
| I worked on a "floating solar" project at Google and you're
| completely correct.
|
| Also, waterproofing is a nightmare, and the panels get dirty
| (salt, algae, bird shit) and stop producing power
| efficiently.
| electricships wrote:
| how much higher is the capex for deep sea floating
| structure ?
|
| (i guess stuff like o&m, grid connection and yield are
| really project dependent)
|
| edit: solar duck just announced 150mw combined pv wind
| project
| cmos wrote:
| I work in Oceanography.. The solar panels on individual
| buoys also get cleaned by rain, and can work ok vertically
| because of reflections. We have special diode bypass panels
| made so if 10% is covered in poop (SeaLion poop in our
| case) only 10% of the power is reduced.
|
| Our biggest problem with small wind turbines on buoys is
| fishingpeople throwing line into them.
|
| But yea, solar for power generation at sea is not
| realistic.. and you are stealing it from the tiny animals
| that make up our carbon sink.
| https://twilightzone.whoi.edu/explore-the-otz/value-of-
| the-o...
| 3dsnano wrote:
| cool way to see the formation of wind farms from above... hornsea
| seems to follow a pattern then it gets all organic looking on the
| left hand side. i wonder why?
|
| my absolute favorite of the wind farms shown is sheringham, a
| true ocean rhomboid. i got curious and found the website for the
| wind farm [1], and here's an aerial view [2]
|
| [1] https://sheringhamshoal.co.uk/about/overview.php
|
| [2] https://sheringhamshoal.co.uk/about/benefits-of-offshore-
| win...
| moxli wrote:
| There is a NGO in Germany (Space-Eye) working with satellite
| images for search and rescue purposes.
|
| I know from some people involved there that they are always
| looking for developers and data scientists.
|
| The main page is in German but the call for volunteers (you need
| to scroll down to "Volunteers for Space-Eye") is in English.
|
| [1] https://space-eye.org/satelliten-erkundung
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(page generated 2024-03-07 23:01 UTC)