Category: Sonar

CHIRP - Shallow Water

2014 Dec 23

With the launch of the new HDS III, CHIRP is now a standard feature and naturally this technology will become more of a hot topic in the New Year. This morning I took the following equipment out on to the water for testing in shallow water to see what this technology has to offer me when I’m fishing for Largemouth Bass. You are not going to find formulas and engineering principles in this article, but if you are looking for more technical information,click here

The primary test was to see how the Gen3 performs with two of the most likely transducers to be used, the $200 HDI (non-broadband transducer) and the $400 Airmar TM150M CHIRP transducer. For good measure I also decided to test a high end CHIRP transducer, the $1500 B175M. The reason I chose the ‘M – medium’ was because I didn’t want to lose coverage area with the ‘H-High’ due to the small cone size. Like everything in life, just when you buy a $1500 transducer, somebody says: “Why didn’t you get the B175H-W?” This is a High CHIRP transducer, but with a wide coverage across the entire frequency range, naturally the correct choice for this application.

I brought the SonarHub along as well just to make sure that the HDS III and the SonarHub are in fact the same ‘sonar engine’, as claimed.

The Goal:

To compare the target separation, coverage area (cone size) and target strength on a simulation (test rig) of two suspended ‘fish’ very close together.

Conditions:

Being summer, we naturally have quite warm water, especially here at sunny Inanda Dam near Durban KZN, South Africa . What is a bit strange for this time of the year, is the deep thermocline, holding a lot of algae in the top 40ft.

To prevent doing tests in the algae, I went to a depth (60’) where the two ‘simulated fish’ would be just below the thermocline at about 42’.

Gen3 / HDI transducer / Medium CHIRP:

This first pass gave good results.

target separation – very good

coverage area - excellent

target strength – reasonable

2 X Zoom – the two targets can clearly be identified as two separate ‘fish’, but the sensitivity was too high at Auto +2.

Gen3 / TM150M:

Medium CHIRP:

target separation – very good

coverage area - good

target strength – reasonable

3 X Zoom:

The water column below the thermocline is very clear.

target separation – very good

coverage area - good

target strength – reasonable

Fixed Frequency: 83kHz 3 x Zoom

target separation – very good

coverage area - good

target strength – reasonable

.

Fixed Frequency: 105kHz 3 x Zoom

target separation – Excellent!

coverage area - good

target strength – reasonable

Fixed Frequency: 155kHz 3 x Zoom

target separation – Excellent!

coverage area - good

target strength – reasonable

Gen3 / B175M

Medium CHIRP:

target separation – reasonable

coverage area - reasonable

target strength – low

Medium CHIRP 3 x Zoom

target separation – good

coverage area - reasonable

target strength – good

Fixed Frequency: 105kHz 3 x Zoom

target separation – good

coverage area - reasonable

target strength – good

Gen3 with SonarHub as sonar source:

I have tried both software versions on two separate units with all three transducers and the results are not even worth posting here as they are terrible. We will get to the bottom of it in the not too distant future hopefully.

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