Sky lapse in two tone(blog.datadesk.eco)

251 pointsby ltrgvor 2 Jahren31 comments

blog.datadesk.eco

https://blog.datadesk.eco/p/sky-lapse-in-two-tone

35 comments

moxlivor 2 Jahren

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

jvanderbotvor 2 Jahren

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)

m2fkxyvor 2 Jahren

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.

fithisuxvor 2 Jahren

Any good source for SAR image formation? From antennas to image processing?

m2fkxyvor 2 Jahren

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-...

fithisuxvor 2 Jahren

thank you very much

enriqutovor 2 Jahren

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.

m2fkxyvor 2 Jahren

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.

enriqutovor 2 Jahren

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?

m2fkxyvor 2 Jahren

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...

notahackervor 2 Jahren

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.

[deleted]vor 2 Jahren

(1)

[deleted]vor 2 Jahren

3dsnanovor 2 Jahren

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...

sparselyvor 2 Jahren

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?

gmanevor 2 Jahren

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

helsinkiandrewvor 2 Jahren

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

The_Colonelvor 2 Jahren

Wikipedia has a short paragraph on the topic with some references for more details: https://en.wikipedia.org/wiki/Wind_farm#Turbine_spacing

DavidPeiffervor 2 Jahren

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...

[deleted]vor 2 Jahren

algo_tradervor 2 Jahren

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_vor 2 Jahren

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_sdvor 2 Jahren

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.

electricshipsvor 2 Jahren

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

cmosvor 2 Jahren

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...

hardlianotionvor 2 Jahren

I had no idea shipping lanes were so densely populated.

EDIT - thanks all. I'll read it next time ...

mysterypievor 2 Jahren

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.

hardlianotionvor 2 Jahren

Yes, you can still see the shipping lanes very clearly.

buzzmvor 2 Jahren

Outstanding link; thanks for sharing.

d1sxeyesvor 2 Jahren

These are composites, although it's not clear exactly how many images are composed to build the final view.

rob74vor 2 Jahren

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...

sokoloffvor 2 Jahren

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.

cricalixvor 2 Jahren

You can look at Marine Traffic to get a better sense of now versus the composites in the article.

louthyvor 2 Jahren

The English channel is apparently busiest shipping lane in the world, so it’s not surprising that it looks so busy on these images.