4 ms·

Most of SentinelHub's open access data comes from Sentinel-1 (radar) and 2 (optical) satellites constellations, which offer a 6-days or shorter revisit time ove

by m2fkxy 5y ago

Most of SentinelHub's open access data comes from Sentinel-1 (radar) and 2 (optical) satellites constellations, which offer a 6-days or shorter revisit time over nearly any point on Earth (for S-1, this is currently longer, as one of the two S-1 sats making up the constellation is out of order). This is not quite high resolution data however - in the 10 to 20 meters per pixel range, i.e. medium resolution. Sentinels are not reconnaissance satellites, but are rather tasked for mapping and collecting large amounts of data globally, for which the main use cases do not necessarily need high resolution imagery (agricultural monitoring, deforestation, natural catastrophes...). Reconnaissance satellites have much finer ground resolution (sub-meter per pixel, down to a couple dozen centimeters... from what is publicly available), and some constellations feature daily revisit cycles.

dylan604 5y ago
>as one of the two S-1 sats making up the constellation is out of order I'm having a really hard time calling 2 dots in the sky a constellation. Does 1+ satellites equate to a constellation in satellite owner/operator parlance?
- arwineap 5y ago
  A fleet is simply more than one ship traveling together, so it seems to translate fine
  - dylan604 5y ago
    In everyday parlance would you say "look at those ships" or "look at that fleet"? That's all I'm trying to say. I didn't say the term was incorrect. I'm just stating that I have a hard time using the term as it just sounds pompous.
    - LargoLasskhyfv 5y ago
      The Sentinels share the same orbit. So far with only one there is a revisit time of 12 days with one, and 6 days with two, with more (planned) even less. But you could have searched that yourself, or not? I wonder what you think of https://en.wikipedia.org/wiki/TanDEM-X https://en.wikipedia.org/wiki/TanDEM-X & https://en.wikipedia.org/wiki/TerraSAR-X https://en.wikipedia.org/wiki/TerraSAR-X ? Would convoy be OK?
      - dylan604 5y ago
        Unless those satellites are sending messages like "10-4 good buddy", you might upset CW McCall[0] for using the term convoy. There are certain words/terms that evoke a vision in one's mind. Convoy just says 18-wheelers. Fleet conjures multiple ships. Constellation conjures more than 1-2 and constantly visible. [0]https://www.youtube.com/watch?v=Sd5ZLJWQmss https://www.youtube.com/watch?v=Sd5ZLJWQmss PS. it's not a matter of what I can or can't look up. People here are too uptight and want to correct everyone else. Sometimes, conversations can be had on not whether a word is actually correct, but whether it leaves one with the right "feeling" (ugh, is that allowed on HN, feelings??).
        LargoLasskhyfv 5y ago
        Yah, well. Now that you are saying it, and seeing the frame from that movie, I probably have seen it sometimes. But it didn't stick. CW McCall didn't ring any bells for me. Convoy is just a saying for many vehicles riding together, almost bumper to bumper. It's done for marriage from some ethnic groups. Or after a soccer game. But it's also said for just two vehicles driving together, at least around here. Sedans and SUVs, no Trucks(Semis?) necessary. (Shrug) And no, feelings are disallowed because 'Resistance is futile!' & 'Prepare to be disassmbled for scanning and upload into the Protomolecule' ;-> (Do these ring any of your bells?)
- m2fkxy 5y ago
  The IAU cites Wood L., 2003 who defines a satellite constellation as "a number of similar satellites, of a similar type and function, designed to be in similar, complementary, orbits for a shared purpose, under shared control" [1]. So, Sentinel-1 is a two-satellite constellation, yes. [1]: https://www.iau.org/public/themes/satellite-constellations/ https://www.iau.org/public/themes/satellite-constellations/, https://link.springer.com/chapter/10.1007/978-1-4615-0431-3_2 https://link.springer.com/chapter/10.1007/978-1-4615-0431-3_...
- contravariant 5y ago
  The mathematician in me thinks it should be fine to have 1 and 0 satellite constellations as well.
  - tremon 5y ago
    Why? Isn't a constellation a shape? What shape can be inferred from 1 point of information?
    - aught 5y ago
      quite a lot actually. Especially that kind
- justsomehnguy 5y ago
  > I'm having a really hard time calling 2 dots in the sky a constellation. Does 1+ satellites equate to a constellation in satellite owner/operator parlance? I'm having a really hard time calling 2 servers in the DC a cluster. Does 1+ servers equate to a cluster in server owner/operator parlance?
  - dylan604 5y ago
    I don't know. Does it? You clearly have the answers.
    - justsomehnguy 5y ago
      > The most common size for an HA cluster is a two-node cluster, since that is the minimum required to provide redundancy, but many clusters consist of many more, sometimes dozens of nodes. You clearly don't have an access to a search engine. [0] https://en.wikipedia.org/wiki/High-availability_cluster#Node_configurations https://en.wikipedia.org/wiki/High-availability_cluster#Node...
      - dylan604 5y ago
        Why would I look up something someone else replied with in snark, or something I don't really care about?
- jazzyjackson 5y ago
  The constellation Canis Minor is made up of just two stars, so it’s true at least in astronomic parlance :)

by m2fkxy 5y ago

dylan604 5y ago

>as one of the two S-1 sats making up the constellation is out of order I'm having a really hard time calling 2 dots in the sky a constellation. Does 1+ satellites equate to a constellation in satellite owner/operator parlance?

arwineap 5y ago
A fleet is simply more than one ship traveling together, so it seems to translate fine
- dylan604 5y ago
  In everyday parlance would you say "look at those ships" or "look at that fleet"? That's all I'm trying to say. I didn't say the term was incorrect. I'm just stating that I have a hard time using the term as it just sounds pompous.
  - LargoLasskhyfv 5y ago
    The Sentinels share the same orbit. So far with only one there is a revisit time of 12 days with one, and 6 days with two, with more (planned) even less. But you could have searched that yourself, or not? I wonder what you think of https://en.wikipedia.org/wiki/TanDEM-X https://en.wikipedia.org/wiki/TanDEM-X & https://en.wikipedia.org/wiki/TerraSAR-X https://en.wikipedia.org/wiki/TerraSAR-X ? Would convoy be OK?
    - dylan604 5y ago
      Unless those satellites are sending messages like "10-4 good buddy", you might upset CW McCall[0] for using the term convoy. There are certain words/terms that evoke a vision in one's mind. Convoy just says 18-wheelers. Fleet conjures multiple ships. Constellation conjures more than 1-2 and constantly visible. [0]https://www.youtube.com/watch?v=Sd5ZLJWQmss https://www.youtube.com/watch?v=Sd5ZLJWQmss PS. it's not a matter of what I can or can't look up. People here are too uptight and want to correct everyone else. Sometimes, conversations can be had on not whether a word is actually correct, but whether it leaves one with the right "feeling" (ugh, is that allowed on HN, feelings??).
      - LargoLasskhyfv 5y ago
        Yah, well. Now that you are saying it, and seeing the frame from that movie, I probably have seen it sometimes. But it didn't stick. CW McCall didn't ring any bells for me. Convoy is just a saying for many vehicles riding together, almost bumper to bumper. It's done for marriage from some ethnic groups. Or after a soccer game. But it's also said for just two vehicles driving together, at least around here. Sedans and SUVs, no Trucks(Semis?) necessary. (Shrug) And no, feelings are disallowed because 'Resistance is futile!' & 'Prepare to be disassmbled for scanning and upload into the Protomolecule' ;-> (Do these ring any of your bells?)
m2fkxy 5y ago
The IAU cites Wood L., 2003 who defines a satellite constellation as "a number of similar satellites, of a similar type and function, designed to be in similar, complementary, orbits for a shared purpose, under shared control" [1]. So, Sentinel-1 is a two-satellite constellation, yes. [1]: https://www.iau.org/public/themes/satellite-constellations/ https://www.iau.org/public/themes/satellite-constellations/, https://link.springer.com/chapter/10.1007/978-1-4615-0431-3_2 https://link.springer.com/chapter/10.1007/978-1-4615-0431-3_...
contravariant 5y ago
The mathematician in me thinks it should be fine to have 1 and 0 satellite constellations as well.
- tremon 5y ago
  Why? Isn't a constellation a shape? What shape can be inferred from 1 point of information?
  - aught 5y ago
    quite a lot actually. Especially that kind
justsomehnguy 5y ago
> I'm having a really hard time calling 2 dots in the sky a constellation. Does 1+ satellites equate to a constellation in satellite owner/operator parlance? I'm having a really hard time calling 2 servers in the DC a cluster. Does 1+ servers equate to a cluster in server owner/operator parlance?
- dylan604 5y ago
  I don't know. Does it? You clearly have the answers.
  - justsomehnguy 5y ago
    > The most common size for an HA cluster is a two-node cluster, since that is the minimum required to provide redundancy, but many clusters consist of many more, sometimes dozens of nodes. You clearly don't have an access to a search engine. [0] https://en.wikipedia.org/wiki/High-availability_cluster#Node_configurations https://en.wikipedia.org/wiki/High-availability_cluster#Node...
    - dylan604 5y ago
      Why would I look up something someone else replied with in snark, or something I don't really care about?
jazzyjackson 5y ago
The constellation Canis Minor is made up of just two stars, so it’s true at least in astronomic parlance :)