single ping overview
========================================================================
== single-ping ADCP data ======
Single-ping raw data files can be read with matlab programs in the
UH CODAS processing suite. The on-line html documentation provides
more detail than is possible here.
Overview:
An ADCP produces records in a binary file. UH CODAS
procssing includes a matlab "read" function for raw data
generated by 4-beam Doppler sonars manufactured by Sontek, RDI
(all, as far as I know, including Ocean Surveyor, Workhorse,
Broadband, Narrowband), and HDSS (50kHz and 140kHz sonars on
the Revelle; this software worked once but is not actively
supported)
Doppler data can be though of as having three stages:
(1) single-ping (highest time resolution) data, straight
from the instrument
(2) single-ping NAVIGATED data, i.e. same time resolution
as #1 but including
- nice features such as UTC time, position, heading, pitch+roll
- NAVIGATED single-ping data comes from a data acquisition
system
(3) averaged (usually averages of #2)
The UH CODAS processing "read" can read most of these.
Details:
(1) raw single-ping data:
For self-contained (moored or lowered) instruments, you
download a file from the recorder. (Although averaging may
take place in the instrument, for the purposes of this
discussion these data are still referred to as "single-ping",
though RDI terminology is more like "single-ensemble". In
any case, this refers to the finest time resolution available
in the data coming from the instrument.
For a direct-reading (shipboard) systems, a data acquisition
system continually obtains the data from the instrument, updating
files on a disk. These data really are single-ping in the
sense that no averaging was done by the instrument.
UH matlab "read" can handle all the raw data mentioned above.
Data in this category are:
- LADCP or moored data (if 4 beams)
- RDI ADCP ENR data collected by VmDAS
- RDI ADCP "raw" data collected by UHDAS
(2) navigated single-ping data:
These come from two sources only:
- VmDAS ENS files (with UTC time and navigation, but
in beam coordinates)
- VmDAS ENX files (with UTC time and navigation,
in earth coordinates)
- HDSS files (with UTC time and navigation, in earth coordinates)
- (UHDAS single-ping data can be loaded with navigation using tools
available in the UHDAS CODAS software)
- (there is no mechanism for reading navigated Transect data)
(3) averaged files:
- LTA, STA (VmDAS averages)
There is no matlab "read" for pingdata (though there is
ping2mat executable)
There is no matlab "read" for Transect averages
---------------
CODAS processing of ADCP data consists of three stages.
(I) read, "navigate" (find UTC time, add position and attitude),
edit, and average the single-ping data
(II) load the averages into CODAS, find and smooth the reference
layer, obtain a gps-based heading correction for the gyro
headings, determine preliminary angle and amplitude
calibrations from watertrack and/or bottom track data (using
corrected headings)
(III) editing (bottom interference, wire interference, bubbles,
ringing, identifying problems with heading and underway
bias), final calibration based on edited data
If you start with LTA, STA, or pingdata, you are starting at (II).
What _used_ to be known as CODAS processing is really steps
II and III. With the access to VmDAS single-ping data, (ENS or ENX)
we have the opportunity to do a better job editing at the
single-ping stage. With UHDAS and HDSS data, we are required
to start with single-ping data.
If you start with single-ping data (stage I), you should already
be familiar with stages II and III.
