Previously I have asked Space based active optical sensors for maritime surveillance. As a follow on, No Synthetic Aperture Radar sensor is allowed. The suggestion is to use an RF scanner and verify that against collected AIS signals.

What kind of RF scanner can be used on the small satellite to detect ships/boats. Is there a COTS product available to do RF scanning from the satellite onto the ocean? Remember, the ships or boats might not have AIS radio as the mission is to detect illegal fishing

EDIT: Do we have any COTS sensors in line with Cubesat that is adapting this concept SEAker?

  • 2
    $\begingroup$ IMHO Problem No1: Doppler shift. AIS signal - only 14kHz wide $\endgroup$
    – A. Rumlin
    Commented Sep 28, 2021 at 17:31
  • $\begingroup$ @A.Rumlin That's a really good idea for most ships, but the last sentence is "Remember, the ships or boats might not have AIS radio as the mission is to detect illegal fishing" $\endgroup$
    – uhoh
    Commented Sep 29, 2021 at 0:07
  • 1
    $\begingroup$ Is "SAR" for Synthetic Aperture Radar? $\endgroup$
    – Ng Ph
    Commented Sep 29, 2021 at 14:50
  • $\begingroup$ @uhoh ok. 1. Take a photo. 2. Determine the coordinates of the borders of the photo. 3 Define all ships in the photo. 4. Ships without coordinates in AIS are the desired ones. $\endgroup$
    – A. Rumlin
    Commented Sep 29, 2021 at 16:04
  • $\begingroup$ @A. Rumlin, the problem at hand is a tad more complicated. The ship that have turned off their AIS to conduct illegal activities do not care much being taken in a photo, as long as you can not proved their IDs. Now photos do not work at night or when the sky is clouded. So when they turn back on their AIS, several hours later, it is difficult to incriminate them. $\endgroup$
    – Ng Ph
    Commented Sep 29, 2021 at 21:32

1 Answer 1


Oh, here is a quirky but interesting idea.

SAR is really taking off as an intelligence gathering capability provided to customers by businesses. In visible light we have the model of Planet Lab providing a rich array of data products at various pricing schemes, in SAR there are several companies starting to do the same. Consider Capella Space and ICEYE and Umbra (also) for example, and even NASA + ISRO joint projects.

See also:

In other words:

There's an ever-increasing number of radar flashlights lighting Earth 24/7!

Perhaps a modest, low cost project can be envisioned that parasitically makes use of whatever SAR beam happens to be hitting a patch of ocean.

Fishing boats contain metal surfaces that can sparkle when illuminated by radio.

Stealthy aircraft avoid 90° internal corners for their propensity to reflect directly back towards the transmitter, but once you relax that condition and receive from a substantially different direction than the transmitter, all bets are off. Now, all kinds of random configurations can have unexpected bright reflections (high radar cross sections) at certain combinations of incident and reflected directions relative to the object.

So for an ad hoc suboptimal but low(er) cost ship presence detector, why not use the reflections produced by other SAR satellites' powerful beams?

We know where both we are and where those are at any moment via TLEs to better than 10 km and we know were most ships are via AIS, so knowing the shape of the Earth and having a delta-t (difference in arrival time) between a weak direct beam and a reflection should allow us to start to reconstruct the positions of the reflections.

It will take some pattern searching to match up constellations of ship reflections to known AIS positions, but these techniques exist (cf. How (the heck) does Astrometry.net work?) Any reflection that doesn't match up with AIS positions is a candidate for further investigation.

SAR beams are certainly mostly focused on the target scan area, but any antenna will have all kinds intensity below -60 to -90 dB in all directions, which will be a similar intensity to weak reflections of the primary beam.

This will take some serious development, but it really could work!


From Star-shaped artifacts in SAR images of the "Suez Canal traffic jam seen from space"

cropped detail from ESA multimedia via Wikimedia: Suez_Canal_traffic_jam_seen_from_space

Source and original ESA source

From Spacenews.com's SAR Renaissance: Pandemic slows but doesn’t stop constellation progress:

From Spacenews.com's "SAR Renaissance: Pandemic slows but doesn’t stop constellation progress" Credit: Euroconsult

Credit: Euroconsult


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