Author Topic: Sidescan quality degrades when using 83 kHz and 83/200 kHz option. (Read 35553 times)

SonarTRX · « **on:** April 10, 2012, 09:25:04 PM »

I have noticed on several sample Humminbird recordings a slight "bar-code" effect (stripes in the data.) It seems like the problem occur anytime the 83 kHz is in use via the sonar menu. (i.e. 83 kHz, or 83/200 kHz option selected.) When the 200 kHz option is in use, there are no such issues.

Has anyone seen this problem before?

The image below - from one of the sidescan channels - illustrates the problem. I also looked at the raw side-imaging data from the sidescan channels, and it seems like the sample values are shifted by 3 elements every second ping when the problem occur. (i.e. every second scan-line is shifted by 3 pixels when the 83 khz is in use)

Perhaps someone from Humminbird who monitor this forum can have a look.
It is easy to reproduce:

1. Start recording
2. While recording, set the sonar frequency to 83 kHz, then 200 kHz and finally 83/200 kHz.
3. Stop recording

When done, view & zoom in on the recorded sidescan data and note that the problem seems to go away while only the 200 kHz is in use. It is easiest to see the pattern close to the surface, along the seabed, or at the edge of features (when the 83 kHz is in use.)

Tore

xSilmarilSx · « **Reply #1 on:** April 11, 2012, 03:24:16 AM »

My take on this:

Since in HB transducer, the same crystal is used by the 200 and the 83 signal, you need to have a trade-off in quality in one or the other.
I presume that HB uses 200 kHz crystal and shoot 83 kHz signal in them. The drawback, is it could cause some interference with the close spaced SI crystal.

To check the previous statement, you should test with 2 transducer. One for the 2D signal and the other for SI, spaced the farther you can on the boat.

Remember, this is pure speculation!

Humminbird_Greg · « **Reply #2 on:** April 11, 2012, 10:26:37 AM »

Humminbird does use the same element to produce both the 200kHz and 83kHz sonar.

Rickard · « **Reply #3 on:** April 11, 2012, 12:45:30 PM »

Tore,

Yes, I have seen the same pattern in my recordings. I mostly use the old SI transducer with 50/200 kHz, but the pattern looks the same. I checked a large number of 50 or 50/200 kHz recordings and they all show this pattern to some extent. None of the 200 kHz only recordings have this pattern.

To me it doesn't look like shifts, I think every second ping is amplified for some reason. But the effect is still disturbing. Unfortunately, there is another recording issue that seems more serious to me. At the 200 kHz only setting gaps occur in the recordings. These gaps are many pings wide so the image can be severely distorted. At 50 or 50/200 kHz gaps are rare, but then there is the "bar-code" instead. I have struggled with the gap issue for at least a year and thought I found the solution... a solution with "bar-codes".

The common element setup could provide a clue. When the same element oscillates at two separate frequencies there must be some risk for interference between the frequency channels.

Rickard

sonar2000 · « **Reply #4 on:** April 11, 2012, 02:06:33 PM »

wow, you guys worry me for SAR decisions.

I am havcing to pay a lot more attention to displays and recordings...

We just cant afford to miss a target...

Hmmmmm. Maybe a change in our SOG's in that we will run a second sonar if the first shows nothing of interest.

We just cant afford to leave a target on the bottom.

chuck

SonarTRX · « **Reply #5 on:** April 11, 2012, 03:47:30 PM »

Hi Rickard and Chuck,

It seems to me that this is a fixable problem (i.e. a software issue) Perhaps there is a bug in the code that samples the data and writes it to the recording. There seems to be an index offset of 3 - or a timing issue for every second sidescan sounding, but only when the 4'th channel is being recorded (i.e. the 83 kHz)

I included a couple of screenshots based on exported raw ping data from SonarTRX. One figure shows the data in Excel, with the alternating pattern showing as soon as the 83 kHz is being recorded (line 12 and on...). The other shows an Excel-graph of the same data (only the very first few sounding samples) Some of the curves are not shifted and some are not. (...half the curves are shifted while the 83 kHz is being recorded)

Rickard: You say you have gaps when using the 200 kHz option only. I agree, but the gaps are just in the 83 kHz channel, right? Here is what is recorded on my 998c-SI based on the sonar frequency settings for the down-facing transducer:

83 kHz : Both 83 kHz and 200 kHz channels are recorded

200 kHz: Only the 200 kHz is recorded - i.e. gaps may occur in the 83 kHz channel if you toggle to this mode during the recording (from any of the other two modes)

83/200 kHz: Both 83 kHz and 200 kHz channels are recorded

Does this match what you have found?

Tore
tore@sonartrx.com

Rickard · « **Reply #6 on:** April 11, 2012, 04:28:57 PM »

Tore,

Very interesting! I think your data and curves prove the "bar-code" shows systematic displacements when recording the 4:th (83 kHz) channel.

The gaps/missing pings occur in all channels, the SI channels too. They are rare when recording all four channels, but common when omitting the 83 (or 50) kHz channel. For a long time I blamed the newer and faster memory cards, but I just found out it was the 200 kHz only setting that caused the problem. I believe a gap occur when the unit stops transmitting in all channels for a fraction of a second.

The image shows an unusually clear example with several gaps when scanning some logs. In most scanning situations the gaps are very difficult to see, but they are there... I wasn't aware of the gaps until I started with scanning under ice with a rotating transducer.

Rickard

sonar2000 · « **Reply #7 on:** April 11, 2012, 04:35:53 PM »

Rickard and Tore.
Do you thing the gap is wide enought to miss a target? (drowning victim)

I am a little concerned..

Chuck

Rickard · « **Reply #8 on:** April 11, 2012, 04:49:33 PM »

Chuck,

I think a gap can cut away part of a drowning victim, but not the whole body. This may distort the image making it difficult to detect the body. So, with quite a bit of bad luck, you may miss a drowning victim.

Rickard

sonar2000 · « **Reply #9 on:** April 11, 2012, 05:00:36 PM »

OK, thanks, was not sure of how wide a gap.
We will be cautious and carefull with our records and reviews.
Extra care if the target is not obvious.

thanks, Chuck

xSilmarilSx · « **Reply #10 on:** April 12, 2012, 02:54:56 AM »

Just a question Chuck... Since you use your units for life threatening situations, should it be wiser to use REAL side-scan sonars. The one made specifically for your field of duty..

I have seen some images and they don't compare to what the small HB unit can produce.
Keep in mind that HB units are only amateur fisherman grade!

Rickard · « **Reply #11 on:** April 12, 2012, 03:59:50 AM »

I must emphasize, "bar-codes" and gaps appear ONLY when recording, not in other modes. This means the display shows gap free images in normal use and snapshots are correct.

Rickard

sonar2000 · « **Reply #12 on:** April 12, 2012, 09:51:00 AM »

Good point SIL.

Two things here:
1) Sonar application is a location and recovery operation. We cant do any rescue..
2) Yes SAR requires several types of sonar units. Not every sonar is one fits the needs unit.
Each sonar has its good points and its limitations. No single sonar will provide all your needs.
To that end, we have 5 different sonar types and use each accordingly.
My concern with HB is that when it does have a place in SAR and if we have gaps then we need to be aware of that and change the way the scan is run. Maybe several passes instead of one or two,
or to move to the second choice of sonar and combine that with the HB run.

Sonar is a science and it is dependent on the skill of the operator and boat driver.

Our job as sonar operators is to say to the "in charge agency for mission" That either a target exists
or that 99% we are sure the target is not in the search area. What we say determines the next step in recovery efforts. If we have a target (great) if not then what needs to be done next?? This is a critical step in the total process.

We have tried over the years to get SAR teams to understand this and if the budget does not afford multiple units then know your neighbor and have a mutual aid agreement..

Thanks for pointing this out..

Chuck

ITGEEK · « **Reply #13 on:** April 12, 2012, 12:43:28 PM »

OK guys, so if I'm not recording, just searching for fish, and I want the very best SI image possible:
Should I keep the conventional sonar set to 200khz?

xSilmarilSx · « **Reply #14 on:** April 12, 2012, 01:00:21 PM »

Thanks for the heads-up Chuck...

It's always interesting to learn more about S&R

ITGEEK · « **Reply #15 on:** April 12, 2012, 07:55:40 PM »

How do you guys know that this is only happening during recording
and not also in real time.
Just to play it safe, I'm only going to use 200kHz for downward sonar.

sonar2000 · « **Reply #16 on:** April 13, 2012, 09:28:23 AM »

ITG, I dont have a clue. that is why we will change our SOG's.....Until this is crisply defined we will have to make sure we do everything possible to find..

I would guess that since we have multiple brands we can apply them also if there is a question.
And of course if the other brand is applicable to the area..sometimes another brand will not be able to produce in a given area..

OH well. At least we have options..

Chuck

Rickard · « **Reply #17 on:** April 13, 2012, 10:48:25 AM »

For natural reasons it's difficult to tell if these issues occur when not recording. Careful inspection requires recording and playback with a computer... But I have observed my unit closely after I discovered the gaps and from what I can see things run smooth in non-recording modes at both 200 and 50/200 kHz. When a gap occur in a recording the display scrolling stops for a brief moment. This causes jerky scrolling if it happens often. When recording stops the image starts to scroll down at a high and even speed. When I tested the system in my bathtub

I could hear the overtones from pings. When recording the sound is stuttering and when not recording the pings come at an even pace. I really don't know what happens to the "bar-code" in non-recording mode and I think the bars are hard to see on the unit display because the pixel resolution is too low for that.
Note, I have gap issues in the 200 kHz only mode, not when I record both downward frequencies (50/200 kHz). But perhaps the gaps are so frequent at 50/200 kHz I can't see them anymore? If that's true they are at least very, very narrow.

Rickard

ITGEEK · « **Reply #18 on:** April 13, 2012, 12:36:43 PM »

From my way of thinking, if you guys can document
SI distortion in recordings when using either the 83kHz by itself or the
combination of 83/200kHz in the conventional sonar, then that's enough to send
up a red flag for me. I'm not going to use the 83 at all.
Plus, I don't fish water that is extremely deep.

The recording gaps at 200kHz don't concern me as much as
the distortion at 83 does.

I just want the clearest real-time SI image.
I'll be using the 200kHz conventional and the 800kHz SI.

I was wondering, have you recorded SI in 800kHz and found
the same types of distortions and/or gaps as 455kHz?

Thanks.

SonarTRX · « **Reply #19 on:** April 13, 2012, 01:57:57 PM »

Yes, the problems occur when recording both 455 kHz and 800 kHz sidescan data (...as long as the 83 kHz is in use.)

Tore

sonar2000 · « **Reply #20 on:** April 13, 2012, 02:41:19 PM »

OK, guys, am I reading you right in that we should set our sonar to 200 and either 455 or 800?
Do not select the 83/200 selection?

chuck

ITGEEK · « **Reply #21 on:** April 13, 2012, 02:57:39 PM »

Chuck,
The way I interpret this is:
If you are recording SI in either 455 or 800kHz,
then conventional 83kHz by itself or 83/200 will cause
distortion in your recordings.
Also, 200 by itself may cause gaps in your recordings.

For just viewing in real time, it doesn't look like the SI is affected,
no matter which conventional you choose.

To play it safe, I'm not going to use 83, either by itself or 83/200.
The gaps in 200 aren't good, but I think I'd rather have small
recording gaps rather than a lot of distortion.

sonar2000 · « **Reply #22 on:** April 13, 2012, 03:00:08 PM »

ITG..thanks..

I looked at the sonar menus.

Is there a way to turn off the 83/200 and use 455/800 only.

I may have missed that in going thru the menu.

chuck

ITGEEK · « **Reply #23 on:** April 13, 2012, 03:26:05 PM »

Chuck,
There are 2 sonar frequency menus on my 1197.

The conventional or beam select has 83, 200, or 83/200.
The SI or side view frequency has 455 or 800.

sonar2000 · « **Reply #24 on:** April 13, 2012, 03:29:49 PM »

Yep,,that is what I have ..but did not see a way to turn off the 83/200 and run only side image at 455/800..

Just checking to make sure I did not miss a selection..

Chuck

Rickard · « **Reply #25 on:** April 13, 2012, 03:36:32 PM »

The unit needs the 200 kHz channel because depth info from that channel is used for automatic setting of ping rate in all channels, also the SI channels. That's why there's no option for turning off 200 kHz.
Rickard

sonar2000 · « **Reply #26 on:** April 13, 2012, 03:38:28 PM »

rickard. forgot about how the depth was obtained. Is that where the water column is determined?
thanks. now I may have to amend my wish list subject..

Chuck

Rickard · « **Reply #27 on:** April 13, 2012, 04:18:41 PM »

Chuck, No, the water columns in the SI views are painted by the SI parts of the system themselves. But since the SI beams are directed at an angle (60 degrees) from vertical they are poor depth sensors. The 200 kHz downward beam is the best source for depth readings.
But I agree with your wish for a no downward beams option. This would require an option for manual setting of SI ping rate, like in professional systems (and in the Lowrances...). To set manual ping rate to something useful the operator will need high skills, though. Manual setting of ping rate is possible with the present HB systems, but only when recording and only up to 10 pings/second.
Rickard

sonar2000 · « **Reply #28 on:** April 13, 2012, 05:59:21 PM »

Rickard, thanks.

Should I add to the wish list, or you can if you want, about the manual ping rate setting also..

chuck

ITGEEK · « **Reply #29 on:** April 13, 2012, 07:15:50 PM »

Chuck,
The idea to not have any distortion in your recordings
is to select the 200 only setting.
Don't select anything with 83 in it for conventional sonar.
But, if you select 200 only, you may get some recording gaps.

I must say that I am very impressed with Tore, Rickard, and xSimarilSx.
I think everybody that has a Humminbird unit should thank them.
As a casual user, I had no idea how the data was recorded.
I assumed everything was OK.

These guys have really gotten into the nitty gritty of the machines.
I think they know more on the workings of these things than
some of the Humminbird engineers that built and programmed them.

I hope Greg is taking notes, so that he can pass the recording distortion/gap info onto the Humminbird engineers. This will allow Humminbird to improve upon their product.

Thanks again guys.
You are the forum scientists.

newkid4si · « **Reply #30 on:** April 13, 2012, 10:15:54 PM »

+ 1 on what ITGEEK said.

Without this forum, what do you think your chances of encountering these people would be,
especially all in one place?
Each poster adds to the general pool of knowledge.

sonar2000 · « **Reply #31 on:** April 14, 2012, 07:18:59 PM »

+1 on the last several posts.

Yes HB should be paying attention to this forum.

there is more good information and help than any other forum I have looked at.
the guys here are willing to help and with great knowledge and experience.

Probably well above the HB help desk...
chuck

newkid4si · « **Reply #32 on:** April 14, 2012, 08:14:10 PM »

Chuck
I would be scared to death to sit at the HB help desk! Think of all the models and software combinations they deal with.
Then consider the people that want the unit to be plug and play. Mount it in the boat, turn it on, and everything works-perfectly.
You and I have hours with our nose stuck in the manual and on this site and we still have issues.Thanks to yourself and others, it normally gets solved.
I have called a few times and have been satisfied with the answers. (A guy should know better than type that last sentence, but no guts no glory)

SonarTRX-- off topic again. I'm 0 an 2 today. Going to read only mode... Sorry

sonar2000 · « **Reply #33 on:** April 15, 2012, 08:34:26 AM »

Yes indeed the challenge is great for the help desk..
consider that most users are plug and play and now without a hardcopy manual I am sure they answer basic questions that tie up their time..
That is why forums such as this are so important.
Questions and knoweledgeable answers are what the user is looking for.
We can generally get an answer out within the day.
And we can teach with the articles and tutorials.
I see this forum as much better in that light over others.
And this is primarily dedicated to the HB units..
Since HB does not have a forum I feel they should support the administration a little better..

Indeed we have a great base of knowledge with those who will share with others.

Chuck

Yes Tore we have kinda hijacked your thread..

ITGEEK · « **Reply #34 on:** April 16, 2012, 01:33:13 PM »

Yea, the Humminbird help desk is great.
Even if they don't know an answer right away.
They will get back to you with the information.

fishshtick · « **Reply #35 on:** May 06, 2012, 02:00:59 PM »

Have there been any further updates on this issue? I get these recording gaps on my 798c all the time. It is particularly common to have them happen right when they are least desired...during depth changes. This tends to exaggerate the depth changes and I became suspicious that there probably aren't that many cliffs in my lake. I also noticed discontinuities in associated bright and dark patches at those drops. So this is clearly a data gap issue. I suspect that when the depth changes relatively quickly, the unit has to adjust ping etc and the processor load is too much for a smooth recording. I am using a Sandisk Ultra 20mb/s SDHC card (class 6). I have not tried turning off the 83 khz channel yet, but will next time out. However, it does not sound like that fully resolves the issue. So in reality is the only solution to not bother recordings and just use snapshots? That's a big negative for me, as I like to review recordings at home to identify structure I may have missed on the water. I think that is something many SI users like to do and if those recordings are screwed up that is going to hurt HB. Likewise, I will sometimes make the unit do a recording while I am viewing other screens, and that does not work with snapshots.

Whistler · « **Reply #36 on:** June 21, 2013, 10:27:36 AM »

Just to continue beating on this horse a bit more...the "zipper" effect issue is ongoing with the most current version of the software (6.640) for my 1198. I can eliminate it by switching the 2D sonar to the 200kHz only beam but both the 83kHz and 83/200kHz beam settings cause a terrible and very noticeable "zipper" effect in real-time on the water use (not just recordings). I'm not exactly sure when this issue reared its head but I believe it was two or three versions ago. It definitely was't there prior to that.

I thought the release notes for 6.640 purported to correct this issue but it has not been corrected. Its really annoying and I hope that it is being worked on.

rnvinc · « **Reply #37 on:** June 21, 2013, 01:56:27 PM »

It started on 6.600 on my 1197 when I updated to use the AS GPS HS antenna ...

Rickie

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