Please explain navigation of NDSF submersibles.
Primary navigation is derived from a Doppler Velocity Log (DVL) system in combination with heading from a high performance inertial navigation system (INS). The INS also reports vehicle pitch and roll. DVL velocities are integrated to estimate dead reckoned position using software (DVLNav) developed by the Dynamical Systems and Control Laboratory at Johns Hopkins University (JHU/DSCL). These estimates are augmented by georeferenced information from ultra short baseline (USBL) and/or long baseline (LBL) acoustic navigation systems. Because the navigation systems of Alvin and Jason are always under human control, correction of DVL drift by resetting to USBL or LBL position in the midst of the dive is routinely performed.
Which should I choose - USBL or LBL?
Long baseline positioning was recommended by NDSF for more than a decade for precise acoustic navigation and survey work. In 2009 a WHOI-developed LBL system, dubbed N456, replaced the Benthos 455 system that had been used for many years. Also in 2009 we introduced into our operations Sonardyne Ranger USBL positioning systems for each vehicle, which can work along with or in place of LBL. In most circumstances, we now recommend use of USBL. Among the advantages offered by use of USBL is a potentially significant savings in setup time. LBL requires the deployment, positional survey, and recovery of a transponder net at each work site, using approximately two hours per transponder. In comparison, a Sonardyne-specified calibration procedure, which is expected to apply for the duration of a cruise, typically requires five hours. When results from this calibration have been applied to a Ranger USBL system, precision and accuracy are comparable to N456 LBL. We continue to use LBL when a preset transponder net exists at a work site. We have also used LBL to navigate Sentry when a dive plan calls for Sentry to perform its survey while Alvin, Jason, or towed camera operations take the ship out of USBL range. When operating in a limited area for multiple dives with Sentry, installation of an LBL net can be a good investment of time.
How do I examine and process NDSF navigation records?
NDSF navigation logs are created by the DVLNav program. See this link, especially for the file describing the formats of all sensor records.
DVLNav logs three basic filetypes:
a. all sensors, native format, native sampling rate.
b. summary files, interpolated to once/second, csv format.
c. configuration file describing sensor positions and alignments.
For lower rate needs, e.g., plotting realtime navigation tracks, use the CSV file. For more demanding needs such as re-navigation or multibeam mapping, use the information in the .DAT files.
For renavigation we extract sensor records by first concatenating all the .DAT files into a single large file, then by parsing the sensor records into separate files. We use the unix utility 'grep', which is available for all platforms.
PNS (Platform Navigation String)
grep PNS infile | grep -v SDE | grep -v LBL | grep -v SHP | grep -v MED > out.pns
RDI (Doppler Velocity Log)
grep RDI infile | grep -v SDE > out.rdi
SDE (DVLNav string log)
grep SDE infile > out.sde
grep OCT1 infile | grep -v SDE > out.ocn
LBL: grep PNS %s | grep NTT > out.lbl
USBL: grep PNS %s | grep OTT > out.lbl
What post-processed renavigation data do I get?
Please see the Data Deliverables section that starts here.
In 2010 we have added other renavigation file formats to support new processing pipelines.
a. Reson Seabat 7125 multibeam system, processed by MB-system (PPL).
b. Various still image capture systems (PPI).
What's the highest altitude at which a survey can be performed?
It depends on the operating frequency of the DVL unit carried by the vehicle. Acoustic energy absorption increases as frequency increases.
300 kHz: up to about 200 meters
600 kHz: up to ablout 110 meters
1200 kHz: up to about 25 meters
At what speeds do the vehicles travel?
Alvin and Jason perform surveys at ~0.25 meters/sec, or 0.5 knots. Sentry performs surveys at 1.0 meters/sec, or 2 knots.
How long do surveys take?
For multibeam, see this page. While NDSF no longer uses the model SM2000 sonar and the information is no longer entirely applicable, much of it is useful.
Photographic survey speed is controlled by camera field-of-view, strobe recharge period, and desired overlap. Camera field-of-view is determined by its optical geometry and altitude. Altitude is in part determined by visibility, and will usually be determined at the start of the survey. Therefore, a survey usually must be designed AFTER altitude is determined experimentally. Obviously, this experimental adjustment can't be done with Sentry.
Example using Jason's downlooking camera system:
|Altitude (m)||F->B FoV (m)||S->S FoV (m)||Speed||Time for 500m trackline (mins)|
What do I need to make copies of Alvin data?
Alvin users will receive about six DVCAM tapes per dive. Users can use the science duplicating system in the Atlantis Main Lab to make backups of these tapes to a variety of media. The science program must provide all media and people power associated with the use of this duplicating station.
At the science duplicating station digital tapes (DVCam or MiniDV from the sphere camcorder) can be cloned or copied to DVCam/MiniDV tapes and also copied to VHS, SVHS or DVD-R media. A deck is available for limited Hi-8 use. There are also Macs available for video editing. During this process a pre-defined data set can be burned into the copies as an overlay if desired.
The correct blank DVCAM media is:
Sony P/N PDV-124N (two hour).
Sony P/N PDV-184N (three hour).
Please remember, as stated on the website: if you are backing up to mini-DV tapes the only type allowed in the duplicating system are Sony and Fuji. Panasonic cannot be used because they are formulated differently and will damage our tape heads.
A filled DVCAM tape will exceed by a few minutes the capacity of DVD or VHS media. To avoid complications from these capacity mismatches Alvin pilots routinely replace DVCAM tapes in the submarine's recorders at just under two hours. Users should bring extra media just in case. High quality DVD-R is the preferred media as inexpensive ones don't always work. Science station DVD video recorders will not use media type DVD+R. Well-regarded brands of DVD media include Taiyo Yuden and Verbatim.
If you want to make copies of the tapes for other PI's and/or your science party bring plenty of your preferred media. On a past cruise the science party made a great cruise highlights DVD with the system but did not bring enough media for everyone to get a copy. Atlantis carries (as of June 2008) a general use DVD duplicator that can perform bulk disc copying. This unit offers more media flexibility than the science station DVD recorders, accepting DVD+R and DVD+RW media in addition to type DVD-R.
Atlantis SSSG technicians are now copying Alvin and shipboard data files to a single external hard drive for the chief scientist. Sharing of the content of this drive can be done using a variety of technologies such as DVD, flash memory drive, or another external hard drive, any of which must brought by the science party. Copying from the chief scientist's hard drive is done by the science party.
On an average Alvin cruise the Chief Scientist will be given 30 - 60 GB of cruise data. For a 15-dive cruise these include approximately:
6 GB of Alvin data
4 GB of Alvin DLVnav data
20 GB of external still camera images
8 GB for science data
If the Reson multibeam sonar will be used storage requirements change dramatically. Raw ping data is produced at about 350 GB per hour.
What are the specifications for the still from Jason's high definition camera?
Resolution: 1920 x1080 x 12 (or 10, sw controllable) bits
Why are the still images from the high definition camera black and white?
It's a single chip camera, so images offloaded from the camera are Bayer-encoded. To turn them into color images, we "demosaic" them using the following call in Matlab:
color = demosaic(j*16, 'grbg')
My Seabat 7125 multibeam maps just aren't coming together. How come?
It might be because you haven't told your processing software that the Seabat 7125 sonar heads face aft on Jason.
In your MB-system script, you'd have:
mbset -F-1 -I datalist.mb-1 -P HEADINGMODE 2
mbset -F-1 -I datalist.mb-1 -P HEADINGOFFSET 180
What's the relationship between the altitude of Jason's altimeter and the downlooking camera?
The downlooking camera can be mounted in a variety of places, so the relationship isn't fixed. The most common camera placement is in the left rear of the vehicle basket. The altimeter is about 10 cm higher than the basket, and about 2.75 meters aft. Jason pitch is about 10 degrees forward, making the altimeter measurement about 0.5m higher than the camera (when placed in the basket). Actual camera altitude can be calculated from altimeter to camera spacing, pitch, and measured altitude.