Topic: Max depth, SI/2D range and recorded ping rate

[matt@reefmaster]

A couple of questions on ping rate, which I know has come up a fair bit on this forum and others, but I haven't been able to find a definitive answer to my question.

Today I took out my new Helix G4N MEGA SI+ for it's first run, and recorded about an hour of data in 3-5m of water, with various settings applied.
Visible range for 2D was always 10m, for SI I varied the range between 20-60m.

Observations in the recorded files:

* The ping rate was ~10 pings per second across all channels, all of the time. When replaying files on the unit, it quotes a 240ms ping which should be enough to cover ~300m of water!
* The recorded depth range for 2D sonar (including DI) was 50m
* The recorded range for SI was a minimum of 50m, increasing only when I increased range manually to 60m (I was mostly running with a range around 20-30m).
* DI quality was poor in my estimation. SI was OK up to 30m, 2D seemed fine but hard to say in such shallow water.

The one setting I didn't change, because I wasn't aware of it, is the overall "max depth" setting in the sonar main menu.

It has long been suggested that depth is the only driver of ping rate on the HB units, so if that is true then I assume the overall "max depth" setting is the one that does this, and the individual sonar ranges under the quick menus do nothing to either ping rate or recorded sonar? I will of course try this as soon as I can, but we have 2 weeks of 30kts+ wind coming up and I am very interested to know the answer now!

If ping rate does indeed increase as hoped, will this reflect in the recording? I am aware of a ping rate setting in the record menu of older units but didn't see it in mine.

Recorded ping rate of course is crucial for resolution along the time axis. I often use Lowrance units to record sidescan data, and routintely get ping rates of over 20/s which is double what I am seeing at the moment with my unit. If anyone has any recordings that were made on Helix units with a lower max depth setting, I would be very grateful if you could share them. I would be more than happy to tell you the ping rate in them! On a related note, I am currently working on improving HB sonar imagery within ReefMaster (HB has been a little neglected in favour of Lowrance recently, but the reason I have just bought a Helix is to fix that). If anyone has any high quality SI recordings that they are willing to share then please get in touch so that we can work something out.

[matt@reefmaster]

I've done a bit of digging through files that users have sent me over the years. I have found G3 Mega recordings with up to a 26 ping per second recorded rate, so it looks like it is (was?) possible. Interesting that these files are also recorded with much smaller sidescan ranges (20m per side). I think I might have to do some experiments in a bucket of water and see what I find.

[rnvinc]

It has always been my understanding that the “Max Depth” setting was only applied in a certain (single) ping “duty cycle” that bottom was not definitively calculated from the return echoes received (as compared to the previous string of ping “duty cycles” received calculating bottom) ...

The “unknown” (to us users) is how often these units actually cannot definitively calculate bottom from the return echoes received in a certain single ping “duty cycle”  ...

Unfortunately we no longer have access to Gregg Walters at Humminbird to delve into the HB mindset  ...

Rickie

[matt@reefmaster]

Thanks Rickie, this also tallies with my understanding (such that it is), but that is only through reading this forum and others. There seems to be a suggestion that "max depth" only makes a difference when the unit doesn't have a firm bottom lock, which was never the case for me yesterday. If that setting doesn't change things for me, then it looks like I am all out of options since I have already set the visible ranges, but I'll take another look at it today. A drop from 26 to 10 pings per second in the recorded file is a dramatic loss of resolution so I really hope I can get it sorted.

[matt@reefmaster]

I spent the morning experimenting with the transducer in a 30 litre bucket of water. Here are some results:



I didn't experiment with every possible setting (pretty sure "detail" is always going to be better than "range" for DI mode).

Observations:

• It is at least possible on this unit to produce recordings with ping rate above 20/s, which is a relief.
• The ping rate appears to be driven entirely by the maximum sonar range that is set within the unit. This in itself isn't surprising, but it is worth noting that it *appears* as if the unit takes the maximum of SI, 2D *or* "Max Depth". So if you are recording with 10m range in 2D and SI but a 20m max depth, you can expect recordings to have a 20m range and the ping rate to be correspondingly lower.
• The recorded sonar range is also driven entirely by the highest range specified. e.g. if you have a 10m range on your 2D but are scanning out to 40m on SI, then the 2D recorded range will be 40m regardless of what is shown on screen. Note: if you want to record some high-res DI, then ensure your SI is set to the equivalent low range to maximise the ping rate.
  
• There is an anomolous result, highlighted in yellow. I can't be sure if I just messed up the settings for this file as there is no way to go back and check. I think that is the most likely explanation.
• To obtain the best resolution for sidescan imagery, you really need to keep the range to 20m or less. This is a little disappointing. 30m gives a 15 p/s rate which is OK but not great.
• 2D, SI, DI frequency and CHIRP on/off makes no difference.
• Chart speed makes no difference, as expected.
• These results don't immediately explain my low (10 p/s) ping rate yesterday when I was never in more than 10m of water. My best guess is that, since I had "Max Depth" on Auto, the unit decided early on to use a value of 60m interally and stuck with it for the duration of the session (all of my channels had a recorded depth of 60m yesterday).

I hope to trial this on the water soon. I have seen files from the G3 (unknown software version) with ping rates over 20/s for SI ranges of 25m. I would like to be able to achieve that. I'm guessing theoretical maximum is something in the range of 25 p/s for 25m range, given 50m round trip per ping and 1300m/s sound speed in water, so in fairness we are not too far off - and these pings must be operating in parallel already?


I still have the transducer bucket set up so if there are any options you think I should try then please let me know.

[tournevase]

hello

if it can help, here some data concerning only the SI :

on a recording, some parameters of the file advantageously displayed by the free viewer "sonarwave lite" are :
-        pings : 2814
-        samples : 4206
-        range : 39,96 m  (this is the range of each side)
-        duration : 4’39”

as the pings generated during the way of the boat create an  image of the bottom, the pings frequency is 2814 / 4'39" = 10 Hz ie each 0,1"

the table of matt shows that the frequency depends of the range something like
range (m) ; freq (Hz)
5 ; 25
10 ; 25
20 ; 20
40 ; 10
the reason is that if the furtherest echoe come back after the next ping, there is a problem

more : the samples are the echoes periodically recorded, so the resolution is 2 x 39,96 x 100 / 4206 = 1,9 cm (4206 is for one side only)
And as 2 x 39,96 m is travelled by the sound at 1500 m/s,  in 53 ms the sampling period should be 0,053 / 4206 = 12,6 micro second and the sampling frequency 79 kHz
but i don't know yet if that frequency is always the same

the cut between two pings is not recorded and so if the space traveled between 2 pings is too large we miss things.
there is therefore a trade-off between the desired longitudinal definition and the time to spend there.
at pings frequency of 10 Hz one ping is emitted every 0.1"
at 5 km/h the distance travelled is 14 cm in 0.1"
at 1 km/h the distance travelled is 2,7 cm in 0.1"
to compare with the transversal definition which is of the order of 2 cm

regarding the screen scrolling
the speed of scrolling on the screen has no automatic link with the speed of the boat but it is wise to adjust it to display the best possible definition
if the scrolling is too slow, the display is compressed and details are not visible ... but fortunatly are recorded for post treatment

and i have a question, matt, how did you calculate the pings frequency ?

     

[matt@reefmaster]

Hi Tournavese,
I actually updated my last post just before you posted yours to highlight the fact that we are probably not *that* far away from the maximum theoretical ping rate, which would be something like 26/s at a 25m range (50m round trip), so results are probably OK.

What is interesting to me is that the max depth really does seem to have a powerful effect here, so it is probably always going to be best to make sure this is as low as your desired sidescan range (or lower). Having SI range higher than max depth is not a problem, the higher range is used.

I have since tried a few other tests, including recording with no SI on screen and background SI pinging set to off. This does indeed produce only DI/2D sonar log files, but even at 10m 2D depth range the ping rate is 25/s, so I think 25 per second may be the global maximum.

I am using my own ReefMaster product to look at the ping rate - this is a value shown for any displayed sonar log files. This is just a crude total pings/total time calculation and I think your table is about right, but with 12.5/s for 40m range. 30m gives 15 p/s and 25m 17.5/s. I think 25m may be the sweet spot for me in terms of coverage/quality, but of course that will depend on the situation. For fishing/on the water use, I don't think a lower ping rate matters too much - the increase in resolution that comes with a higher ping rate really only becomes visible on a large screen. I've also seen some excellent sidescan recorded as low as 5 pings/sec, but of course we always want the best that we can achieve!

Edit to add: your sonar file stats show a ping rate of almost exactly 10 (pings / total seconds), which tallies well with the results I have seen for 40m range. In fact, you can go to 60m and still achieve 10/s.

[tournevase]

in fact, to obtain the longitudinal definition is given by the speed of the boat (not the screen scrolling speed) wich must be matched with the ping rate.
for example, if the longitudinal distance between 2 pings is 1 m then a 50 cm fish located between the 2 pings  will not be seen

so
hight boat speed => hight ping rate mandatory
low boat speed => low ping rate possible

the lateral definition is in all the cases (to be checked) around 2 cm by sample


 

[matt@reefmaster]

I don't disagree, but even 2 knots (very slow) is 1m/s, which would give a max of 10cm resolution at 10 pings/sec ping rate. 20 pings/sec would give double the resolution at the same speed, or allow you to scan at 4 knots for the same resolution. It will always be difficult to control a boat slowly enough to give the maximum theoretical resolution that the beam shape allows if there are only 10 pings per second..

[tournevase]

you are right matt

here after the max possible range function of the pings frequency
over the line, the furtherest echoe come back after the next ping



and



there is a compromise to find

for my surveys in rivers  5 km/h (man walking) and range 40 m will not be so bad

the default setting is ping rate at 10 Hz  for a range of 40 m
is it possible to set ping rate at 15 Hz for a range of 40 m ?

[oschi]

is it possible to set ping rate at 15 Hz for a range of 40 m ?

right + left = 40m or one side only 40m?

These are my mximum pps with transducer max depth setting at 10m. One side only. (Helix 9 MEGA+ SI G4N)



40m one side you could expect a max ping speed of slightly above 12.5 pps.

For best Image quality:
transducer max depth 10m
range max 10m
speed 1.7 kph (if you want "square pixels")

[matt@reefmaster]

the default setting is ping rate at 10 Hz  for a range of 40 m
is it possible to set ping rate at 15 Hz for a range of 40 m ?

Unless I am missing a setting on the G4, then I don't think it is possible.
The G4 seems to allow quite a lot of space between pings, using perhaps 75% of the time available (e.g. 20 pings/s at 20m = 800m round trip, SOS in water ~ 1300m/s).

I have files from the G3 with ping rates of just under  19/s for 32.5m average range (split between 30/35), which is 1235m roun trip and means the unit must be pinging SI almost continuously. I don't know if it is possible to achieve this same ping rate in the G4. If not, why not? Is there a setting, or have they changed the software? A shame if so. I have multiple G3 files from around 2018 that show this higher ping rate behaviour, but I don't know what firmware was used to record them.

Oschi, I don't think one side/both sides makes any difference to ping rate. Your pps rates are in line with my own observations - unfortunately definitely slower than the max pss achieved under earlier versions of the Helix/firmware.

[tournevase]

oshi,
the range is always for 1 side only

These are my mximum pps with transducer max depth setting at 10m

how did you find these values, calculation, settings, product data, ... ?

For best Image quality: transducer max depth 10m range max 10m

when the measured depth reach 10 m what is displayed ?

in fact i don't understand why there is to set some max depth because the max depth able is the vertical SI beam i.e. the SI range choosen

[oschi]

how did you find these values, calculation, settings, product data, ... ?

I bulit my own system that's connected to the Helix network. That calculates the actual ping rates too.
I tested live all different settings to get the highest ping rate and also calculated the range vs. ping rate offline with the recorded data.

in fact i don't understand why there is to set some max depth because the max depth able is the vertical SI beam i.e. the SI range choosen

Range or depth is the same for back scatter measurement. SI, DI and 2D pings are done simultanously (at least the time value is the same for each 3). So if you leave your max depth at e.g. max. 330m you will get that slow ping rates (approx. 1pps) for 10m SI range also, even on 2m water. A waste of time and image quality.

[matt@reefmaster]

Interesting stuff Oschi, and your measurements are exactly the same as mine. Which unit are you using, and which firmware? (I am G4N SI+ with 2.6.60, I think!). Did you try measuring ping rates with older units/firmware? I am still interested in why the ping rates seem to be slightly lower now than they have been in the past with the G3 units (and perhaps others before). It may not seem like much, but e.g. a jump from 15 to 20 p/s for 30m range would give a 33% increase in resolution along the time axis, or allow you to scan that much faster for the same resolution. I wonder if there is anyone at HB we can ask about this?

I have had mixed results with max depth. It seems that it doesn't *always* increase the recorded range/slow the ping speed, but it does sometimes - and it can do this even when it is obtaining good bottom lock in shallow water. It is definitely best to keep this set manually to the lowest depth you can at all times. It is also important not to leave your SI range high if you are hoping for good DI ping rates, as the DI ping rate will slow to your SI range - e.g. if you have in 10m of water you could achieve 25 pings/sec DI but if your SI range is high (likely), then you won't. It's a shame the DI can't ping at it's own speed based on depth, since shallow water/high SI range is a common combination. Perhaps this is a hardware limitation, but it does means your DI will be limited when using SI in normal ranges.

[tournevase]

I bulit my own system that's connected to the Helix network.

great ! 

did you found the sampling rate in the side direction ?
with a range of 40 m, i found around 79 kHz corresponding to a resolution of 1,9 cm

[matt@reefmaster]

great ! 

did you found the sampling rate in the side direction ?
with a range of 40 m, i found around 79 kHz corresponding to a resolution of 1,9 cm

This lateral resolution depends on the speed of sound in water and does not vary with range. It is usually just over 50 returns per metre so your figure is accurate.

[MT]

It is also important not to leave your SI range high if you are hoping for good DI ping rates, as the DI ping rate will slow to your SI range - e.g. if you have in 10m of water you could achieve 25 pings/sec DI but if your SI range is high (likely), then you won't. It's a shame the DI can't ping at it's own speed based on depth, since shallow water/high SI range is a common combination.

This might be the reason for the option to disable SI ping while in background. I was assuming it was for processor relieve, but this explanation makes more sense since enabling or disabling this option doesn't seem to make any difference in unit behaviour.

I like to have SI pinging in background because it allows for sidewiew history display at any time, and i had no clue it could slow 2D ping rate. I'll do some testing to figure out if it's worth to either disable background pinging or leave it and set range to 10-20 m.

[newkid4si]

This is not a hijack of this post, but an opportunity for me to share a thought. Rickie brought up a name from the past---Gregg Walters . Both he and Rickie are giants in the world of quality HB information. We are truly blessed with both. I miss HBGreg.  I'm done.

  Mike

[rnvinc]

I also miss Gregg  ... he personally accelerated my learning curve in those early years  ...

His email at Humminbird is no longer valid. I hope he retired ...

I haven’t talked to him in several years  ...

Rickie