Kherson Bridges – radar, analysis and imagery

I’ve been following the developments around Kherson, Ukraine, with interest over the last week or so. Particularly the attempts by the Russian forces to protect two bridges from attack after both were targeted and damaged by Ukrainian forces.

The two bridges across the Dnipro River are just short of 6 kilometres apart from each other with the western Antonivskyi bridge used for road traffic, and the one to the east for rail.

The Antonivskyi road bridge was attacked on 20 July 2022, and then further on the 27th. The second attack effectively took the bridge out of commission and a temporary – and somewhat dangerous with the equipment being used – pontoon ferry system was put in place by the Russians.

The attacks were carried out using M142 High Mobility Artillery Rocket Systems (HIMARS) with each GMLRS GPS/IMU guided rocket (six per five-tonne Family of Medium Tactical vehicles (FMTV) 6×6 truck chassis) fitted out with a with a 90 kg warhead. CEP accuracy is between two and ten metres depending on the warhead variant being used.

The rail bridge was attacked on 28 July, again using HIMARS.

There’s been plenty of coverage on the internet regarding the attacks – The War Zone for instance – so I’m not going to repeat anything here.

I’m more into looking at the corner radar reflectors the Russians have put in place next to the bridges, and whether they’re really any use in protecting the bridges.

The first reports of the reflectors came out not long after the attacks, and to be honest at first I thought they were old navigation aids – which these reflectors can be used for. But it turns out they have been installed by the Russians. I am slightly confused as to why they have done this.

These reflectors can be used to “draw” enemy radar guided missiles to them rather than a potential target – i.e a building or ship. To be effective you need a certain number of them to encourage the missile to the reflectors rather than this target. There is a mathematical equation that calculates their design and number needed. It is easier for you to go to Radartutorial that explains this in great detail, rather than me repeat it here.

Corner reflector composed of three triangular surfacesRadartutorial

As well as the number needed to encourage the missile, they ideally need to be grouped together and, more importantly, as high up as possible.

On missile target barges used by many navies there are a considerable number of these corner reflectors of various styles, in very close proximity to each other – and generally all on masts. This is as well as being on the very solid metal barge. These create a huge radar return for missile tests.

What the Russians have done at the bridges is almost the complete opposite of this. They have put them at near water level, not on masts, not grouped them, nor put that many out – and they aren’t really that well constructed. By this I mean, whilst they have created reflectors with four “sides”, they don’t appear to have a bottom plate – which, with this missing, greatly reduces the reflection!

As you can see in the image above from Radartutorial, the three sides are needed for a good radar reflection. What the Russians have done is create a pyramid out of four of the above – without the base. And, with their placement, half the pyramid is pointing in the wrong direction to be effective anyway. Moreover, the direction of flight from a missile also determines the reflection created, which is why you need a large number of reflectors pointing in various directions (if the proposed attack angle is not known – which it isn’t here).

The target barge above has 22 reflectors on it, along with wire mesh and likely some emitting antennas as an extra attraction. This is on something about 30 metres in length.

The Kherson bridges, on the other hand, are about 950 metres long for the road bridge and 500 metres for the rail bridge. This is just the river crossing lengths. You could add extra length to this if you include the parts over land. From satellite imagery, the rail bridge has just 6 reflectors in place!

There’s plenty more I could say about this to show the potential missile defence attempt made here by the Russians is pretty well pointless. More so because all of the attacks carried out by HIMARS don’t even involve a radar and the Ukrainians don’t have a missile capability as such anyway!

It just isn’t worth the effort. The bridges will always create a bigger radar return than the reflectors.

When SAR imagery from Sentinel showed the rail bridge with a “ghost” bridge alongside it, I wasn’t convinced this was what the Russians were trying to achieve either. Though they do have it as an option as @The_Lookout_N pointed out.

This is pretty old school though and in modern warfare where near immediate satellite imagery is available – pretty pointless. You will notice though, that image three in his tweet shows the very same reflectors used at the bridges. You’ll also notice that they are grouped together. The main task here is to imitate a pontoon bridge rather than a large rail or road bridge.

Below is a sequence of Sentinel SAR imagery from 25 July, 29 July and 5 August respectively.

You can see that the reflectors have made very little impact. It is obvious there are bridges there, and that they emit a huge radar reflection, especially the rail bridge due to its construction design.

The second image from 29 July was the one that many thought was a “ghost” bridge to confuse SAR. Taking a look at the 25 July imagery you can see a small reflection west of the bridge. This measures between 30 and 40 metres in length – the same as the barges being used further down river. A return approximately the same size is in the 29 July imagery around the reflectors. I think this is a barge being used to install the reflectors.

In the later imagery this return has gone and is actually a little back down river at the point where a new barge crossing has been put in place.

Sentinel SAR is ok, and it has its basic uses, but when you step into full High resolution satellite imagery you can see the “ghost bridge” attempt is pointless.

First I’ll start with Capella Space 50 cm resolution SAR.

Here I’ve made a collage of several images taken over the week. As new ones have appeared I’ve updated them, but I had to call it quits eventually, so here are 5 images put together into one. They are dated from 25 July 2022 to 3 August 2022. The bridges are covered by the 3rd August and was right along the edge of the collection, hence a little bit of interference.

The actual file is huge – over 480MB – therefore I can’t put it up here, so I had to shrink it down to 10% of the actual image I created to get it to fit. It is still good enough to show the reflectors, the barge crossings etc.

Close ups of the bridges on 3 August clearly show the reflectors, potential pontoon ferries and also likely damage caused by the HIMARS attacks.

When we look at 28 July 2022 EO imagery of the rail bridge from Planet – again at 50 cm resolution – you can clearly see the reflectors and damage to the railway just south of the bridge.

One round has certainly hit the rail line, whilst a couple of others just missed.

Zooming in to the image gives us a better look at the damage.

The interesting aspect of the damage is the target area. As discussed above, the bridge is large, with a large radar reflection cross-section. But we also stated that the Ukrainian forces don’t have a missile strike capability for targets such as this.

So why target this area of the bridge?

Two reasons.

Firstly, the bridge provides its own defence against weapons such as HIMARS thanks to its design. The metal frame structure would likely stop a GMLRS round from hitting the rails – statistically it would have to be an amazingly good shot to get through the gaps in the frame.

Of course, the metal structure would likely be damaged, but it may not make the bridge unusable.

Secondly – and this is more important than point one – they have targeted the concrete upright rather than the rail itself. Why is this important?

In the image below from 1 August 2022, it does appear that the damage to the rails has been repaired. However, it may not have been finished, or good enough to use, as just outside the image a pontoon ferry system has been set up to either cross the river directly, or to move equipment up and down river.

Typically, my selected area just cut off the pontoon ferry operations, but we know they are taking place from other EO imagery available – and it can be seen in the Capella imagery above.

However, had the HIMARS strike hit the concrete upright, this would have brought the whole rail line down in that area, would have been near impossible to repair – certainly quickly – and would have made the bridge totally unusable.

The craters that are left are just a couple of metres away from the upright. The hit to the line was near directly on top of it. HIMARS has a two metre CEP – it is that close an unlucky miss.

All this proves, though, that a radar guided weapon is not needed to strike these bridges.

The road bridge is totally out of action. The rail bridge is within a couple of metres of being the same.

All in all – very strange defensive measures have been put in place for these bridges – especially so as the Russian forces have much better anti-missile defence equipment available to them.

They still don’t seem to have any answer to HIMARS however.