DOI: 10.5061/dryad.k3j9kd5k7
title: Direct measurements of 4-dimensional variability in oceanic flow structures with a new towed phased array Doppler sonar

description: Abstract from the manuscript associated with this submission (Direct
 measurements of 4-dimensional variability in oceanic flow structures with
 a new towed phased array Doppler sonar):  A Towed, Phased-Array
 Doppler Sonar (TPADS) has been developed. Using a phased array approach we
 form a fan of beams over a ~110 degree aperture that allows us to measure
 radial ocean velocities in three dimensions. The use of modern analog to
 digital converters developed for medical ultrasound enables a compact
 instrument that can be mounted on a small towed body, which allows us to
 isolate the instrument from the motion of the ship. The compact nature of
 the instrument also enables significant flexibility in deployment
 parameters. Here we describe this instrument and show two case studies
 from early deployments. The first shows the three dimensional shear field
 near the bottom in a region of complex bathymetry with slopes
 near-critical to the internal tide. We capture the three dimensional
 structure of shear layers that slope along internal tide characteristics.
 In the second case study we deploy TPADS in a surface scan mode that
 enables high precision measurement of ocean surface velocities. We show
 measurements of surface velocity across a sharp density front with
 horizontal resolutions of ~15m. An asymmetric frontal jet with a scale of
 ~500m is measured. TPADS promises to be an important tool in the study of
 small-scale and three-dimensional instabilities on the ocean surface and
 in the bottom boundary layer, which are hard to observe with conventional
 acoustic Doppler techniques.
description: # Direct measurements of 4-dimensional variability in oceanic flow
 structures with a new towed phased array Doppler sonar
 \[[https://doi.org/10.5061/dryad.k3j9kd5k7](https://doi.org/10.5061/dryad.k3j9kd5k7)] ## Description of the data and file structure This set of data and scripts is provided alongside the manuscript "Direct measurements of 4-dimensional variability in oceanic flow structures with a new towed phased array Doppler sonar" to fulfill data availability requirements. Any data used to generate figures in that manuscript are included, as well as code to process data from raw, depth binned velocity estimates for each of the two main modes of operation discussed in the manuscript, normal-scan and surface scan. All code written by Devon Northcott ([dnorthco@ucsd.edu](mailto:dnorthco@ucsd.edu)) and Austin Green ([a7green@ucsd.edu](mailto:a7green@ucsd.edu)). Data is from the towed phased array Doppler sonar (TPADS) and auxiliary sensors. Most data is full rate depth-binned velocities. Data from the Downlooking deployment is geolocated and binned.  Data comes from three separate TPADS deployments. All data is in NetCTD format;  NetCTD can be read in python using the netCDF4 or Xarray packages, or in matlab instructions on how to open NetCTD files in matlab using their high level NetCDT functions. 1. A surface scan deployment in the Norwegian sea in support of the ONR funded Northern Oceans Rapid Surface Evolution experiment, October 2022. 2. A downlooking normal-mode deployment from a test trip over the Coronado escarpment, San Diego, in June 2023. 3. A sidelooking normal-mode deployment from the ONR funded Arabian Sea Transition Layer field campaign, Bay of Bengal, June 2024. ### Files and variables #### File: Data.zip **Description:**  **Astral_NormalScan_Supporting.nc:** Contains auxiliary data streams from the TPADS fish that are required for TPADS processing, including IMU, CTD, and GPS data from the ONR funded Arabian Sea Transition Layer DRI, June 2024 in the Bay of Bengal. Paired with sonar data in the file Astral_NormalScan_TPADS.nc. VectorNav VN100 data is in the array frame. +y is in the steered direction, toward the nose of the fish, +z is normal to the array, away from the fish. +x in the non-steered direction, up. All times are UTC. **Dimensions:** * ctd_time: Seabird 49 CTD time. UTC. * vnanv_time: Vectornav VN100 time. UTC. * gps_time: GPS sytem time. UTC. **Variables:** * ctd_time: time base for the seabird 49 CTD. * temperature: ocean temperature in degrees C from the seabird 49. * pressure: pressure in dbar from the seabird 49. * depth: depth in meters from the seabird 49. * salinity: Practical salinity in psu from the seabird 49. * accel_time: time base for the VectorNav VN100 IMU. * pitch: pitch in degrees in the array frame of reference. VN100. * roll: roll in degrees in the array frame of reference. VN100. * yaw: yaw in degrees in the array frame of reference. VN100. Unreliable due to magnetic interference. * accel_x: acceleration in g's in the array frame of reference. VN100. * accel_y: acceleration in g's in the array frame of reference. VN100. * accel_z: acceleration in g's in the array frame of reference. VN100. * gps_time: time base for the GPS system. * latitude: ship latitude in degrees from the GPS system. * longitude: ship longitude in degrees from the GPS system. **Astral_NormalScan_TPADS.nc:** Contains TPADS Doppler sonar data from the ONR funded Arabian Sea Transition Layer DRI, June 2024 in the Bay of Bengal. Paired with motion and orientation data in Astral_NormalScan_Supporting.nc. **Dimensions:** * beam: Radial beam number, beam 16 points normal to the array. * range: Range along-beam from the array. * time: start time for each ping, UTC. **Variables:** * beamangle: Beam angle in degrees counter-clockwise from array normal viewed from the behind. Negative angles are up. (beam 16 = 0 degrees) * range: Range along-beam from array in meters. * time: time of ping, UTC. * vel: Radial velocity in m/s. * int: Intensity of sonar return in squared counts. * coh: ratio of coherent intensity to intensity. Typical values between 0 and 1. Values below 0.5 indicate data with low signal to noise and are typically removed. **ASTRAL_NormalScan_WH300.nc:** Contains RDI Workhorse 300 data processed using UHDAS from the ship mounted Doppler sonar aboard the R/V Thomas G Thompson. From the ONR funded Arabian Sea Transition Layer DRI, June 2024 in the Bay of Bengal. **Dimensions:** * time: time, UTC * depth: depth in meters **Variables:** * time: time, UTC * u: East-West ocean velocity. * v: North-South ocean velocity. * latitude: ship latitude in degrees. * longitude: ship longitude in degrees. * z: depth in meters. **Downlooking_Binned.nc:** Contains data from the down-looking normal-scan deployment that is used in figure 7 in the manuscript. This data was collected as part of a June 2023 test trip aboard the R/V Byster near Coronado Escarpment, San Diego CA. Data is geo-referenced and binned. **Dimensions:** * Crosstrack: Cross-track distance, defined perpendicular to the ship course over ground. * Alongtrack: Along-track distance, defined parallel to the ship course over ground * Depth: Depth in meters * Bottom_track_beam: Radial beam number. in this deployment configuration, the fan of beams is oriented perpendicular to the ship course. * Bottom_track_time: Bottom depths are estimated for each ping. Each sample represents one sonar ping. **Variables:** * lat: bin latitude in degrees. * lon: bin longitude in degrees. * depth: bin depth in meters * v_shear: Vertical derivative of cross track velocity. * bottom_track_lon: bottom track sample longitude in degrees. * bottom_track_lat: bottom track sample latitude in degrees. * bottom_depth: bottom depth in meters below surface. * fish_lon: ship longitude in degrees. * fish_lat: ship latitude in degrees. * fish_depth: fish depth in meters. **SurfaceScan_Raw.nc:** Contains range binned Doppler sonar data from the October 2022 Surface scan deployment as part of the ONR funded Northern Oceans Rapid Surface Evolution Experiment in the Norwegian Sea. Orientation data is in the fish frame. +x is along the fish axis, positive aft, +y is across the fish axis, positive port, and +z is positive up. Array is mounted on the port side of the fish, beampattern parallel to the fish motion, and pointed 16 degrees up from horizontal. Data from the Seabird 49 CTD and Vectornav VN100 IMU is subsampled onto sonar timestamps. **Dimensions:** * Beam: Radial beam number, beam 16 points normal to the array. * Range: Range along-beam from the array. * Time: start time for each ping, UTC. **Variables:** * beamangle: Beam angle in degrees counter-clockwise from array normal viewed from the above. Negative angles are forward. (beam 16 = 0 degrees) * range: Range along-beam from array in meters. * time: time of ping, UTC. * pitch: Pitch in degrees, fish frame. * roll: Roll in degrees, fish frame. * yaw: yaw in degrees, fish frame. Unreliable due to magnetic interference. * lat: ship latitude in degrees. * lon: ship longitude in degrees. * pres: fish pressure in dbar. * vel: Radial velocity in m/s. * int: Intensity of sonar return in squared counts. * coh: ratio of coherent intensity to intensity. Typical values between 0 and 1. Values below 0.5 indicate data with low signal to noise and are typically removed. * vel_corr: Radial velocity in m/s corrected for estimated fish motion. * surf_Temp: Surface temperature from ship underway CTD system. degrees C. * dp_dt: Change in fish depth vs. time, dbar/s. ## Code/software \[[https://doi.org/10.5281/zenodo.14846020\]](https://doi.org/10.5281/zenodo.14846020) Matlab is required to run these scripts, they were created using version 2024b.  Surf_Vel_from_nc.m: Processing script for surface scan data. Generates figure 8 from the manuscript. NormalScan_Astral_fromNC: Processing script for normal-scan data. Runs comparison between TPADS derived shear estimates and RDI WH300 derived shear estimates. Generates figure 6 from the manuscript. Utility: Various scripts that are required the run the two data processing scripts above.