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Tag: satellite

Sun-synchronous orbit

by Timothy Whitehead on Jun.14, 2016, under 3D Models, Argentina, Australia, Brazil, California, Denmark, England, Germany, Google Earth News, Google Earth Tips, Google Sky, Google maps, Hawaii, Indonesia, Ireland, Italy, Japan, Kenya, Mexico, Natural Landmarks, Netherlands, Sightseeing, Street Views, USA

In yesterday’s post we suggested that the reason for the near polar orbit of most imaging satellites was to improve coverage. After a bit more research it turns out to be more interesting than that. Apparently there is a special orbit called Sun-synchronous orbit, which is designed such that the satellite always crosses a given latitude on the ‘day’ side of the Earth at the same time of day. This has two benefits:

  • if two neighbouring images, or images of the same location are captured on consecutive passes of the satellite, they will have the same lighting (both the overall brightness as well as the length and direction of shadows), which makes it much easier to stitch them together in the case of side by side images or comparing for changes in the case of images of the same location.
  • the orbit can be positioned such that the satellite is always overhead as close to noon as possible (or whatever time is considered the best for imaging) for the latitudes of greatest interest. A non Sun-synchronous near polar orbit would result in some days when the satellite is orbiting in a plane at 90 degrees to the direction of the sun, which would make it constantly sunrise or sunset.

A Sun-synchronous orbit has a particular inclination depending on the altitude of the satellite. The lower the altitude, the closer the orbit is to the north-south direction. For a table of altitude vs. maximum latitude, and other technical details, see Wikipedia.

As far as we can tell almost all imaging satellites are in Sun-synchronous orbit, including SkySat-1 and SkySat-2. They also all have altitudes in the 500-900 km range, meaning they should all have similarly tilted orbits with a maximum latitude of around 82 degrees.

Thank you to GEB readers franksvalli2 and Vasilis for letting us know that the mystery image in yesterday’s post is almost certainly from one of the SkySat satellites. See this PDF file for details on those satellites, including their sensor arrangements which creates the distinctive ‘Y’ pattern. Also thank you to GEB reader Daniel Plant for bringing our attention to TeLEOS 1, which, as you can see here has a very different orbit.

We used our circle drawing tool to estimate the orbit of the satellite that took yesterday’s image and it came remarkably close to the expected 82 degree maximum latitude.

Although DigitalGlobe imagery in Google Earth is typically in both vertical and horizontal stripes, we believe that the imagery is actually captured by a satellite following a Sun-synchronous orbit very similar to the Sky-Sat orbits. We believe that the almost perfect north-south or east-west alignment of the DigitalGlobe strips is for some reason other than orbit. We have noted in the past that they line up with degrees of latitude and longitude.

For more interesting reading about orbits see this article from NASA.

The post Sun-synchronous orbit appeared first on Google Earth Blog.

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Time-lapse videos from Himawari-8

by Timothy Whitehead on Jul.15, 2015, under 3D Models, Argentina, Australia, Brazil, California, Denmark, England, Germany, Google Earth News, Google Earth Tips, Google Sky, Google maps, Hawaii, Indonesia, Ireland, Italy, Japan, Kenya, Mexico, Natural Landmarks, Netherlands, Sightseeing, Street Views, USA

Google Maps Mania recently had an interesting post about time-lapse videos of Earth from space captured by a Japanese weather satellite named Himawari-8. Check them out on the Himawari-8 website here. In addition to the time-lapse videos, the website’s homepage features a near real-time view of the earth. In addition, you can scroll through images for the past week. There are two possible views selectable from the menu at the top left. There is a view of just the Japan region with images every two and a half minutes and a view of the whole globe with images taken at 10 minute intervals.


View from Himawari-8 at noon. The time shown is Japan time (UTC +9).

It is important to note, however, that Himiwari-8 is a geostationary satellite and so it always has the same view of the earth, which in this case is centred above the equator to the south of Japan. Geostationary satellites have the advantage of being able to monitor a single view continuously. In addition, geostationary orbits are so high (35,786 km approx.) that it is possible to take an image of the whole world at once (from a particular angle). Most high resolution imaging satellites, such as those that provide most of the imagery for Google Earth, are in much lower orbits (typically 400 – 600 km) and travel at such fast speed that they can only view a particular location for a few minutes, as we saw with the UrtheCast videos. They still fly over the same location on earth once a day or more, so longer term time-lapses are still possible.

Google Earth’s weather layer includes a near real-time cloud layer that comes from weather satellites similar to the Japanese one. If you check the ‘information’ sub-layer of the weather layer you can download a 24 hour animation of the clouds viewable in Google Earth.

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BlackSky Global

by Timothy Whitehead on Jun.22, 2015, under 3D Models, Argentina, Australia, Brazil, California, Denmark, England, Germany, Google Earth News, Google Earth Tips, Google Sky, Google maps, Hawaii, Indonesia, Ireland, Italy, Japan, Kenya, Mexico, Natural Landmarks, Netherlands, Sightseeing, Street Views, USA

Last week we had a look at UrtheCast, a satellite imaging company that has just released their first videos captured from the International Space Station.

Today we are looking at another satellite imaging company called BlackSky Global. They have not yet launched any satellites, but plan to launch six satellites in 2016 and have a 60 satellite constellation by 2019. For more details see their press release.

They are not the first company to plan a large constellation of imaging satellites. Last year we talked about a company called Satellite which had very similar plans and launched their first satellite in June 2014. However, there is no sign of any progress from them since then. Skybox Imaging, which is owned by Google, also plans a large fleet and already have two operational satellites.

Most of the above companies have or are planning relatively cheap satellites with a resolution of about 1m and focusing their marketing message on their ability to capture frequent images. Google Earth gets most of its imagery from DigitalGlobe, whose best resolution satellite WorldView-3 has a resolution of 31cm. Google also gets some imagery from Airbus Defence and Space (listed as CNES/Astrium in the copyright information). However, their best satellites seem to be SPOT 6 and 7, with a resolution of 1.5m.

The global image used in Google Earth when zoomed out comes from Landsat 8, which has a resolution of 15m.

The best resolution imagery in Google Earth is aerial imagery. However, many parts of the world only have satellite imagery, and even areas with aerial imagery usually do not have frequent updates and could benefit from a greater availability of satellite imagery. We have been hoping to see Skybox imagery in Google Earth but are not aware of any being featured so far.

With the addition of BlackSky Global, the future of satellite imaging looks good.


BlackSky’s Pathfinder spacecraft, one of its first satellites.

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Satellogic planning to achieve global coverage with live video and pictures

by Timothy Whitehead on Oct.28, 2014, under 3D Models, Argentina, Australia, Brazil, California, Denmark, England, Germany, Google Earth News, Google Earth Tips, Google Sky, Google maps, Hawaii, Indonesia, Ireland, Italy, Japan, Kenya, Mexico, Natural Landmarks, Netherlands, Sightseeing, Street Views, USA

Yesterday we talked about Skybox, which is owned by Google and currently has two satellites, but is planning a constellation of 24. When we talked about their gif animations of the Burning Man festival, we also pointed out a YouTube video that they say is the first HD resolution video of Earth from space. More videos from Skybox can also be found here

We recently came across this interesting article about a startup, Satellogic, that is planning to launch hundreds of satellites and provide live video and regular pictures with global coverage.

From their website:

We are building a constellation of satellites to image any spot on earth every few minutes.”

It won’t be as high resolution as the best images from Digital Globe, and we must remember that at any given time much of the globe is obscured by cloud cover, but global coverage with live video or pictures every few minutes is still exciting stuff!

BugSat-1 in a clean room
BugSat-1 in a clean room.

The internals of a satellite
The internals of a satellite.

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DigitalGlobe launching their WorldView-3 satellite today

by Mickey Mellen on Aug.13, 2014, under 3D Models, Argentina, Australia, Brazil, California, Denmark, England, Germany, Google Earth News, Google Earth Tips, Google Sky, Google maps, Hawaii, Indonesia, Ireland, Italy, Japan, Kenya, Mexico, Natural Landmarks, Netherlands, Sightseeing, Street Views, USA

worldview-3DigitalGlobe, one of the leading providers of imagery for Google Earth, is launching their new WorldView-3 satellite in a few hours. It is scheduled to launch at 11:29am PDT today from Vandenberg Air Force Base, and you can watch a live broadcast of the launch here.

The new satellite will feature some great enhancements over previous ones, including:

  • Will capture imagery at 31 cm resolution, the highest available resolution on the market. This allows you to see not only a car, but the windshield and the direction the car is going. Something as small as home plate can be seen with 31 cm resolution.
  • Due to its shortwave infrared sensor, the satellite can actually image through haze, fog, dust, smoke and other air-born particulates.
  • Beyond crop mapping, this satellite will actually be able to identify moisture levels, differentiate between healthy and unhealthy crops, and even classify species on the ground.
  • The satellite can identify types of minerals on the earth’s surface
  • It can identify not only a tree’s class and species, but its health as well

It should be a great step forward for imaging, and ultimately for Google Earth. Check out the infographic below for an overview of the satellite, visit worldview3.digitalglobe.com for more information, and watch the launch live in a few hours.

worldview-3-infographic

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The next generation of satellites for Google Earth

by Mickey Mellen on Feb.17, 2014, under 3D Models, Argentina, Australia, Brazil, California, Denmark, England, Germany, Google Earth News, Google Earth Tips, Google Sky, Google maps, Hawaii, Indonesia, Ireland, Italy, Japan, Kenya, Mexico, Natural Landmarks, Netherlands, Sightseeing, Street Views, USA

To understand how images make it from satellites in orbit to Google Earth, you should take a look at Frank’s excellent about Google Earth imagery post from a few years ago. In short, Google doesn’t own any satellites that capture imagery; they buy the imagery from providers such as DigitalGlobe.

With that in mind, Richard Hollingham of the BBC took a trip to Ball Aerospace in Boulder, Colorado, where the WorldView-3 satellite is currently being assembled for DigitalGlobe.

WorldView-3

WorldView-3 will be able to capture imagery at a remarkable resolution of just 25cm, though only the US government can purchase imagery that detailed. For Google Earth (and similar mapping projects, such as Bing Maps), the imagery will be released at a resolution of 50cm. As the article points out, from more than 600km away, travelling at around eight kilometres per second, capturing an image half-a-metre across is an impressive technical achievement, and is less likely to raise concerns about privacy.

It’s an excellent article that shows a bit more about how things work in regards to satellite imagery, and I recommend you check out the full story for yourself.

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