The Chinese maritime surveillance system

[ExNusquam]

Sunburn, last I checked the DSP satellites aren't actually importable (the platform exists, though). I just assumed this was just due to the fact that the actual longitudes of the birds being classified. Additionally, the SBIRS birds in game have extremely limited detection capabilities. They don't seem to detect lauches, and the IR sensor they have has a detection range of only 2000NM, which means that anything beyond 33°N/S is undetectable to them from geostationary orbit. Additionally, the launch detection doesn't seem to work well. Try running the attached save.

[BradOrbital]

This should help, see attached. Cloud history for a good few years.



Clouds can be funny though. We sometimes have a (what seems) completely clear area but right on top of the object we wanting to look at ends up being a freaking cloud. Nature has a serious sense of humour.

[Dimitris]

ORIGINAL: ExNusquam
Sunburn, last I checked the DSP satellites aren't actually importable (the platform exists, though). I just assumed this was just due to the fact that the actual longitudes of the birds being classified. Additionally, the SBIRS birds in game have extremely limited detection capabilities. They don't seem to detect lauches, and the IR sensor they have has a detection range of only 2000NM, which means that anything beyond 33°N/S is undetectable to them from geostationary orbit. Additionally, the launch detection doesn't seem to work well. Try running the attached save.

Thanks for the heads-up, we'll look into both of these.

[gosnold]

On the subject of plane detection with DSP and SBIRS, I read in America's space sentinels, a book on the history of those programs, that DSP detected Iraqi planes on afterburner during GW1. I think that the the only Iraqi planes with afterburners at the time were fighters, so it seems the satellites can detect quite small signatures (though I Iraq had Mig-25s and they have quite big engines).

[ziolo]

Very interesting!

[jmax]

Awesome, thank you so much!

In a similar vein, does anyone have some good info on Chinese SOSUS and OTH radar?

[mikmykWS]

Hi Guys

Thanks for all the info. I've been looking through our Chinese sat orbat and there is some work to be done. Public info is a pita btw. The Gaofen-4 is supposed to be in a geostationary orbit over Singapore more or less but public orbital data doesn't have it near there. We'll do our best to rectify this but we can only work with what we have and unfortunately we need better data on some.

We've got one critical issue that needs to be solved in that we don't yet define the area that a sat can see. We just do slant range, zoom detection and zoom classification. So the result is a very high sat with values that can see to the ground will also be able to see a very large swarth of territory which isn't quite right. We know what the issue is and are working on a solution.

The next phase at some point will be looking at is focus. Sats don't just see thing but people have to be looking for something in the imagery they produce so we've got to refine that logic a little more. We're thinking about that as well.

Thanks!

Mike

[gosnold]

ORIGINAL: mikmyk

Hi Guys

Thanks for all the info. I've been looking through our Chinese sat orbat and there is some work to be done. Public info is a pita btw. The Gaofen-4 is supposed to be in a geostationary orbit over Singapore more or less but public orbital data doesn't have it near there. We'll do our best to rectify this but we can only work with what we have and unfortunately we need better data on some.

We've got one critical issue that needs to be solved in that we don't yet define the area that a sat can see. We just do slant range, zoom detection and zoom classification. So the result is a very high sat with values that can see to the ground will also be able to see a very large swarth of territory which isn't quite right. We know what the issue is and are working on a solution.

The next phase at some point will be looking at is focus. Sats don't just see thing but people have to be looking for something in the imagery they produce so we've got to refine that logic a little more. We're thinking about that as well.

Thanks!

Mike

Glad to know you are improving the satellite modelling! You are right that with the current one Gaofen 4 (which the latest spacetrack TLE do put in GEO over singapore btw) would be able to see everywhere all the time. You can fix that by including local weather (to block its view in some regions), by including angle limitations (if the satellite is too low over the horizon its resolution is degraded, so it can only look at the area below it, and not at the poles for instance), and by including swath width constraints with the focus mechanism as you have described. Scenario designers can also include detectable but not identifiable civilian traffic, to confuse the player. Overall however, a high-resolution imaging satellite in GEO is an extremely powerful tool.

One way you could model swath width is by having a detection probability depending on the area to be searched. Basically a satellite can only look at x km2 per minute. So if you ask to look for a target in an area of x km2, the detection probability is 100% * the usual probability calculation.
If you ask to survey an area of 2x km2, the detection probability drops to 50% of normal, and so on.

I have an excel table of observation satellites, with their resolution, swath width and orbits when available, which you can use as a starting point:
https://dl.dropboxusercontent.com/u/108 ... 0sats.xlsx
The data mostly comes from eoportal, but it's more synthetic.

Another aspect you might want to consider is agility: old satellites can only point in one direction, and so if you give them two focus area far apart they can not image both. The new ones can. Here's an example of Gaofen 4 showing the use of agility:



Typically for a GEO imaging sat it takes in the order of minutes to repoint it to another area, that's what limits your ability to image everywhere all the time.

[Dysta]

One new GEOSTAT meteorological satellite, FengYun-4, is now orbiting.

https://www.nasaspaceflight.com/2016/12 ... engyun-4a/

[tomrlutong2]

Gognold, thanks, this is an amazing post full of great information. Like Gunner98, I went from having a vague idea of sat. capabilities to feeling very well informed thanks to you. I'll now use this new knowledge to ask a stupid question.

The Gaofen-4's infrared resolution is 400m. Solar isolation in orbit is 1366 W/m^2. So, there's 218MW of solar energy falling on each Gaofen-4 IR pixel. From wikipedia, the reactors in the Nimitz class are rated at 550MW (thermal). My understanding of civilian PWRs is that they can't operate below 20% of full capacity.

So, at full power, a Nimitz is generating 1100MW of heat, and at lowest power 220MW. That's equal to or greater than the amount of solar energy falling on a GF-4 pixel. Does that mean that in all circumstances, a Nimitz would be detectable by infrared?

[gosnold]

That's a good question. The answer is a bit more complex than your calculation:
- The solar insolation is partly absorbed by the sea (some of it is reflected), and reemitted at different infared wavelengths (which depend on sea temperature).
- The thermal power produced by the reactors on the Nimitz heat the sea around the ship (especially in its wake), and thus the sea radiates at different wavelengths.
- The ship itself is not at the same temperature as the sea.
- The atmosphere absorbs part of the infrared radiation

So the computation is not straightforward. A good tutorial on these issues is there

A back of the envelope computation using the https://en.wikipedia.org/wiki/Stefan%E2%80%93Boltzmann_law gives an irradiance of 10W/m^2 for a (black) body at 10°C, so that could be the background irradiance. That's 1.6 MW for 400m^2, so the heat output of the Nimitz should be detectable with good contrast even if it is spread on several pixels. (edit:corrected computation mistake)

Another interesting question is: could Gaofen-4 detect aircrafts on afterburner (likely yes, american DSP satellites can do it and they have a 1km resolution), or even standard jet engines (maybe).

[ExNusquam]

ORIGINAL: gosnold
Another interesting question is: could Gaofen-4 detect aircrafts on afterburner (likely yes, american DSP satellites can do it and they have a 1km resolution), or even standard jet engines (maybe).

Theoretically, but we don't know the exact sensor design of the GF-4, so it might be of much use tracking aircraft.

DSP is a non-imaging scanning sensor that checks it's FOR every 10-seconds. This is great for missile warning across an entire AOR. The GF-4 sensor is probably analogous to the SBIRS-GEO Staring sensor. From a US OSD Report:

The GEO staring sensor will have high agility to rapidly stare at one earth location and then step to other locations,with improved sensitivity compared to DSP. Several areas can be monitored by the staring sensor with revisit times significantly smaller that that of DSP. A continuous staring mode will also provide an even smaller revisit time.

These sensors are probably more useful in the Technical Intelligence/Battlespace Characterization roles than an Indications and Warning (IW) role. If China launches a scanning sensor to tip-and-cue the GF-4 onto events, I think the IR sensor will become far more useful. That would allow the scanner to detect the event and the starer to characterize/track it. Currently I think it's used to supplant the EO sensor during night hours.

[gosnold]

Actually we know quite a bit about the GF-4 sensor:

[Dysta]

Jilin-1 Satellite debuted a short geo footage of Bogota airport.

http://www.chinadefenseobservation.com/?p=5011

[gosnold]

Reviving this thread as the Chinese have launch a new kind of constellation, focused on very high revisit:
Article on satelliteobservation
It's probably ELINT, and if so would provide nearly continuous coverage.

Also I have reformatted my database of observation satellites, it's now there (and the documentation there.

[Dimitris]

This is great stuff, thank you!

[Dysta]

ORIGINAL: gosnold

Reviving this thread as the Chinese have launch a new kind of constellation, focused on very high revisit:
Article on satelliteobservation
It's probably ELINT, and if so would provide nearly continuous coverage.

So what it’s called to be exact, YG-30-01 or YG-31?

http://www.spaceflightinsider.com/organ ... ite-aloft/

[stilesw]

gosnold,

Many thanks for this reference. I've added it the the unofficial Dropbox CMANO reference library.

Anyone who would like to be added to the access list please PM me with your email address.

Currently over 200 items and 50 members.

-Wayne Stiles

[gosnold]

I'm reviving this thread with two updates:

One on TJS-4 a Chinese SIGINT satellite in geostationary orbit:
https://satelliteobservation.net/2019/11/20/tjs-4-the-ears-of-beijing/

And the other on the a (probably SIGINT) Yagoan-30 constellation in low earth orbit:
https://satelliteobservation.net/2019/11/04/some-news-on-the-yaogan-30-constellation/

[gosnold]

The Yaogan-30 constellation has been reinforced with new launches and is now complete:

https://satelliteobservation.net/2020/11/25/china-completes-the-yaogan-30-constellation/