# Open space location at sea

Hi,

Sealartec Ltd. is a new company developing solutions for the automation of launch and recovery systems of USVs (Unmanned Surface Vehicles at sea).
We are looking for a way to determine the relative position between 3 floating bodies at sea (all are positioned close to each other).
We normally have, one big platform such as a ship and two small platforms such as small boats.
We mainly wish to determine the relative position between the 2 small boats.

The position we wish to monitor is in the range of 0.5m to 30m. Accuracy of under 10% of the measured distance may be sufficient.
We can install the sensors and other system components above the water line.
Line of sight is always clear.
We wish to be able to work under rain conditions as well.

Does any of Decawave products may suite our needs?

Thanks,

Hi Amitai,

The UWB technologie can suit your application. Depending on the RF configuration, the range can be > 100 meter with an accuracy < 30cm.

In order to calculate a position, there are mainly two approach:

[list]
[]Calculate a device position relatively to a fixed infrastructure (4 anchors)
[
]Calculate the bearing and distance of a device relatively to a fixed point (1 anchor), providing a relative position.
[/list]
In your application, I guess the larger boat could be the reference for both smaller boat and it would provide the boats coordinates relatively to it.

I would recommend to buy some of the Decawave development kit (EVK or MDEK) to implement a proof of concept.

Thank you,
Best regards
Yves

Hi Yves,
I have a few more questions:

Can you tell us what will be the expected accuracy in 10m range and in 2m range?
Is there a minimum distance that the system can measure?

When you say: “bearing and distance of a device relatively to a fixed point (1 anchor)”, does that mean that:
Assuming that I am only using 2 small boats. And I position the anchor on boat number 1 and I the other component on boat number 2.
Will I get the distnace and relative angle of the position of boat 2 relative to boat 1?
Or will I get the distance of boat 2 from boat 1 plus the direction that boat 2 is ‘looking’ at boat 1?

What is the main difference between EVK or MDEK

Thanks,
Amitai

this range bias effect

Hi Amital,
The distance measured is proximity , the distance between the two node. so not direction or phase difference of arrival. One should develop this application as all the two way ranging software delivered free of charge is based on two way ranging. PdoA SW is available at request but there is a fee attached to it.
But when direction required also, one would need at least three nodes for localisation (and direction) So in your case a TREK1000 could be used for initial evaluation.
The accuracy is not related to range so it would be at least +/- 10cm, irrespective of the range.
There is no minimum distance , but to close (<0.5) it might lead to distortion , range bias errors

Finally, the difference between TREK and EVK is on high level described in the presentation attached. Note, for more detailes on the difference I recommend you read the briefs or user manuals of both products.

/Leo