Bathymetric Lidar

[Tobias Filskov Petersen]

Dear All, 

In general, how would you run a classification of a point cloud if you were to classify bottom returns (from the seafloor or a stream) and how would you locate the water level. Is it possible using LAStools?

Best regards. 

Tobias 

[Martin Isenburg]

Hello Tobias,

would be nice to develop such a workflow. But is seems there is a lack of publically accessible bathymetric LiDAR data for people to experiment with. I have gotten repeated inquiries for open bathymetric LiDAR data sets that would allow folks to get skilled in processing bathymetric data. Can you share (parts of) yours or do you (or anyone else) know of such data available for download anywhere?

Regards from Dubrovnik,

Martin @rapidlasso

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[Kirk Waters - NOAA Federal]

There are a number of topobathy data sets freely available the on NOAA Digital Coast, https://coast.noaa.gov/dataviewer. Most of the newer ones have been classified, but there are still some from mid-2000s that are really just classified as green-laser returns (we used class 11). Lidar cleaning and classifications is a topic on the agenda tomorrow at the JALBTCX Airborne Coastal Mapping and Charting Technical Workshop (JALBTCX is Joint Airborne Lidar Bathymetry Technical Center of eXpertise). You could always unclassify the data to play with if you wanted. There are at least 60 datasets with bathy available.

Kirk Waters, PhD                     | NOAA Office for Coastal Management

Applied Sciences Program      | 2234 South Hobson Ave
843-740-1227                          | Charleston, SC 29405    

coast.noaa.gov/digitalcoast

[Jorg Hacker]

Hello Martin and Tobias,

Just about all of our bathymetric lidar data is available (for free) for testing algorithms and developing workflows.We have a whole collection of bathymetric lidar from several places in Australia and will add a lot more over the next 3 months when we will fly a large mapping project in North-Eastern Australia and another one in North-Western Australia - all of it in pure research-based applications.

To see some of the existing results, just have a look at our website www.airborneresearch.org.au . There was also an article in one of the recent issues of GIM about our bathymetric lidar. 

If anybody is seriously interested to get their hands on data from bathymetric lidar in just about any form, just contact me at j...@airborneresearch.org.au. As long as that person is prepared to share the outcomes of their tests and developments, there is no problem making data available.

All of our bathymetric lidar is from the Riegl VQ820-G and most of it has data from a Riegl Q680i-S with it. For most of the data, there are also DSLR RGB aerial images available.

Regards from Gumeracha,

Jorg

[Rick Pryce]

Kirk,

 

I just had an opportunity to use some of the NOAA 2016 Bathymetric Lidar for a Survey Project in Miami at Baker’s Haulover cut. It worked out well for what I needed and we were able to test the bottom elevations against actual elevations in the field. The resulting test of the bottom and seawall elevations were within the accuracies stated in the metadata. See attached

 

We had soundings from FDOT running out to about 50 feet from each seawall and that matched the bottom elevations within +/- half foot.

 

We needed the bottom cross-sections for a proposed directional drill bore and this worked out perfectly for that purpose. With the strong currents that run through that inlet, we would have had a difficult time getting the information we needed form our small boat and echo sounder.

 

Richard D. Pryce, PLS/PSM

Vice President Survey & GIS

 

Craven Thompson & Associates, Inc.

3563 NW 53rd Street

Fort Lauderdale, FL 33309

Tel: 954.739.6400

Cell: 954.651.5942

rpr...@craventhompson.com

[Tobias Filskov Petersen]

Hello Martin, 

Thank you for your reply. By time I hope to see such a workflow! :-)  

The acquired data set is unfortunately not mine to share.

Best regards, 

Tobias

[Jorg Hacker]

Hello Kirk,

As I have never before seen bathymetric Lidar data except the one that I collected myself with our Riegl VQ820-G around Australia, I downloaded a sample from the NOAA Digital Coast. It's nice, but I am wondering if it would be possible to access the uncleaned pointcloud data before anything was done to it. That would be really interesting. Our own data is available in any form from totally uncleaned to cleaned and classed (for cases where we did that).

Regards,

Jorg. 

[Kirk Waters - NOAA Federal]

Jorg,

We usually don't see the raw product. In fact, we hope not to see it since that product is generally not useful to the end user. I think the raw information varies considerably by sensor manufacturer too. Many of the sensors will deliver waveforms that are then processed to extract points. Some will do the point extraction in hardware so you never see most of the waveforms. I think Riegl does this. Until the data gets to a certain point, it likely isn't much use unless you have the software for that sensor. I think there is probably a point in the processing between the raw waveforms, IMU, and GPS data and the final classified point cloud that you would call uncleaned, but do you think you could describe it? For example, is this before or after you take into account refraction at the surface? I might be able to look into options then, at least in cases where the government is operating the sensor.

Kirk Waters, PhD                     | NOAA Office for Coastal Management

Applied Sciences Program      | 2234 South Hobson Ave
843-740-1227                          | Charleston, SC 29405    

coast.noaa.gov/digitalcoast

[Christopher Crosby]

OpenTopography also has a few bathy lidar datasets available. All datasets were collected and processed by NCALM.

Optech Aquarius: 

Eel River Critical Zone Observatory: http://opentopo.sdsc.edu/lidarDataset?opentopoID=OTLAS.122016.26910.1b

IML Critical Zone Observatory, Sangamon River, IL: http://opentopo.sdsc.edu/lidarDataset?opentopoID=OTLAS.122016.26916.1b

IML Critical Zone Observatory, Clear Creek: http://opentopo.sdsc.edu/lidarDataset?opentopoID=OTLAS.122016.26915.1b (full waveform data also available on OT)

Niobrara River, Nebraska: http://opentopo.sdsc.edu/lidarDataset?opentopoID=OTLAS.102016.26914.1b

Kremmling, CO: Blue and Colorado River Confluence: http://opentopo.sdsc.edu/lidarDataset?opentopoID=OTLAS.022015.26913.1

Optech Titan (data from green 532nm channel):

Tushar Mountains, Utah: http://opentopo.sdsc.edu/lidarDataset?opentopoID=OTLAS.052016.26912.3b

Greys River, WY: http://opentopo.sdsc.edu/lidarDataset?opentopoID=OTLAS.052016.26912.2b

In addition, a few of the newer NCALM datasets collected with the Titan system have all three channels present - data were delivered in LAS 1.2 using a custom laser channel encoding in the User Data record that is described in their survey reports (see metadata page). E.g., Sea Grass Beds, Apalachicola, FL: http://opentopo.sdsc.edu/lidarDataset?opentopoID=OTLAS.102016.26916.1 

Thanks,

-cc

--
Christopher Crosby
Geodetic Imaging & OpenTopography Project Manager
UNAVCO, Inc. 6350 Nautilus Dr., Boulder, CO 80301

303.381.7564 (o)  |  480.220.3200 (c)

cro...@unavco.org
http://www.unavco.org
http://opentopography.org

[Jorg Hacker]

Thanks Kirk, and also thanks Chris for pointing me in the OpenTopography direction. I will check out these links.

We probably use quite a different workflow than other operators of bathymetric lidars. We start with the raw data from the Riegl VQ820-G and Q680i-S and use Riegl software (including waveforms) to generate pointclouds in scanner coordinates. Then we use our own software to geo-reference all points in the pointcloud. This cloud obviously contains a lot of noise from various effects (bubbles, fish, sediment, and even whitecaps above the waterline). Then we use lastools, our own tools and interactive visualisation procedures (for instance the Lidar module of GlobalMapper) to identify the sea surface and a first guess of the bottom of the water column. With this knowledge, we are able to eliminate a lot of the "noise". Then we apply the refraction correction to the points below the water (including approximate wave shapes). This is a rather slow process and we are working on algorithms to speed it up. Then we use more interactive visualisation to identify the seafloor and features on it more accurately. Finally, we use lasground_new to class the points on or near the seafloor. As this is an interactive process, it is usually a bit  time consuming, but it works very well and the results are very nice.

I should also say that we are often flying multiple overpasses over the same flightlines, sometimes with different scanner settings which assist us in feature identification under water, or to identify schools of fish, etc. We also use quite narrow line spacing. To align the data for the multiple overpasses and/or the overlap (overage), we use Bayesmap Stripalign rather successfully.

An example of this procedure can be seen in the January edition of GIM.

So to answer your question, Kirk, I am wondering if your data providers are also generating geo-referenced pointclouds (with or without refraction correction) before eliminating noise points. If yes, that's the data I would be most interested in.

You also pointed to a workshop about bathymetric noise reduction. Is there a report available, or presentations or similar ? I would be most interested in that.

Regards,

Jorg.    

[Gottfried Mandlburger]

Dear all,

I would like to share some general thoughts from my own experience with
topo-bathy lidar, which mainly is with inland, running water bodies
(i.e. rivers).

As Jörg already pointed out the main challenge in bathymetric lidar (and
the main difference to topgraphic lidar) is: (i) reconstruction of the
water surface and (ii) range and refraction correction. Refraction
correction is pretty straight forward (Snells' law) but keep in mind
that the flight trajectory is required as the refraction correction
relies on the beam direction (to be more precise: the incidence angle
between the laser beam and the water surface normal direction vector).
Identifying and reconstructing the water surface is often not trivial.
And there is no "one-for-all" solution to this problem: Why?

(a) Depending on the roughness of the water surface, the number of
air-water-surface echoes depends on and varies with the surface
roughness. More interface returns can be expected from rough surfaces
(wavy coastal waters), but Jörg has already pointed out the "white cap"
problem which is is not limited to coastal waters but may also occur at
fast-runnning streams. Considering that most bathymetric scanners employ
a constant off-nadir angle of 15-20° (Palmer scanner) the high degree of
specular reflection at smooth (water) surfaces results in many laser
echo drop-outs. This means, that only a few points are available for
water surface reconstruction. The good news: In this case only a few
points are necessary as the surface is smooth anyway.

(b) The water surface may either be dynamic (costal waters, mountain
streams, etc) or rather static (lowland rivers, lakes in case of no or
moderate wind). In the dynamic case the water surface reconstruction
needs to be carried out for each flight strip independently and for
static water surfaces data from all overlapping flight strips can be
used for reconstructing the air-water-interface. In the ideal case
return from the surface and the bottom is available for each laser
pulse. However, in practice this is an illusion and there may well be
pulses delivering an interface echo but no bottom return and vice versa.
I just mention it, as one might think that refraction correction could
be done on a per-pulse basis (without explicitly modeling the water
surface). From my experience this is infeasible. Another argument for
the necessity of modeling the water surface that the assumption of
horizontal water surfaces is no longer state-of-the-art, but proper
refraction correction takes the local water surface slope into account.

This having said, I strongly belief that different procedures are
required depending on the actual state of the water body.

To come back to the main thread of this discussion (available data),
there is sample data (trajectory and raw point cloud, Riegl VQ-880-G)
and the respective workflow available as a use case example of the TU
Wien software OPALS at:

http://geo.tuwien.ac.at/opals/html/useCase_ALB_Pielach_River.html

Data is courtesy of Riegl but can be freely used for non-commercial
purposes.

Kind regards,
Gottfried

PS: Most of my research is "open access", so in case you are interested
just google for: Mandlburger lidar bathymetry

--
Dr. Gottfried Mandlburger

Tel.: +43 1 58801 12235
Fax.: +43 1 58801 12299
http://www.ipf.tuwien.ac.at
_____ _____ _____
/____// ___// / Vienna University of Technology
// __ / /__ / // / Department of Geodesy and Geoinformation
//__/// /__ / // / Research Groups Photogrammetry and Remote Sensing
/____//____//____/ Gusshausstrasse 27-29, A-1040 Vienna

> coast.noaa.gov/digitalcoast <http://coast.noaa.gov/digitalcoast>

>
>
> On Wed, Jun 7, 2017 at 8:17 AM, Jorg Hacker
> <jorg....@airborneresearch.com.au <javascript:>> wrote:
>
> Hello Kirk,
>
> As I have never before seen bathymetric Lidar data except the
> one that I collected myself with our Riegl VQ820-G around
> Australia, I downloaded a sample from the NOAA Digital Coast.
> It's nice, but I am wondering if it would be possible to access
> the uncleaned pointcloud data before anything was done to it.
> That would be really interesting. Our own data is available in
> any form from totally uncleaned to cleaned and classed (for
> cases where we did that).
>
> Regards,
> Jorg.
>
> On Wednesday, June 7, 2017 at 8:35:11 PM UTC+9:30, Kirk Waters
> wrote:
>
> There are a number of topobathy data sets freely available
> the on NOAA Digital Coast, https://coast.noaa.gov/dataviewer

> <https://coast.noaa.gov/dataviewer>. Most of the newer ones

> have been classified, but there are still some from
> mid-2000s that are really just classified as green-laser
> returns (we used class 11). Lidar cleaning and
> classifications is a topic on the agenda tomorrow at the
> JALBTCX Airborne Coastal Mapping and Charting Technical
> Workshop (JALBTCX is Joint Airborne Lidar Bathymetry
> Technical Center of eXpertise). You could always unclassify
> the data to play with if you wanted. There are at least 60
> datasets with bathy available.
>
> Kirk Waters, PhD | NOAA Office for
> Coastal Management
> Applied Sciences Program | 2234 South Hobson Ave
> 843-740-1227 | Charleston, SC 29405

> coast.noaa.gov/digitalcoast <http://coast.noaa.gov/digitalcoast>

[Kirk Waters - NOAA Federal]

Jorg,

I'm pretty sure they do create the point clouds before eliminating noise points. For the post-Sandy data the NOAA/NGS had flown by Dewberry and Quantum Spatial, the different types of noise were classified. I tossed most of the noise points in what we serve because is doubled the size of the data, but the data do still exist. 

The JALBTCX workshop just ended last week, but the presentations will be put online. Pick 2016 on http://shoals.sam.usace.army.mil/Tech_Workshops.aspx to see last year's presentations. This year we tried to have a bit more of an open discussion about classifications and cleaning. I think we'll see more open discussions in the future, so I'd encourage you to join next year. The JALBTCX leads were soliciting ideas for those open discussion topics and I think they'd be happy to hear from you. I'll forward your emails on to them too.

Kirk Waters, PhD                     | NOAA Office for Coastal Management

Applied Sciences Program      | 2234 South Hobson Ave
843-740-1227                          | Charleston, SC 29405    

coast.noaa.gov/digitalcoast