In order to process data from a velocity shear probe the speed of the instrument or flow over the probes must be obtained. When using a Vertical Microstructure Profiler (VMP) the pressure data can be used to determine speed. However, pressure data cannot be used to obtain speed when profiling horizontally with a MicroRider. In most cases, speed must be determined by using an secondary source such as an acoustic doppler velocimeter, an electromagnetic flow sensor or speed records from an AUV or glider.
If your Rockland instrument is mounted on a vehicle that provides mission files, you may wish to integrate the data provided in the mission file into your data processing. In some cases the data recorded by the vehicle is required to process the p-file. There are currently four scripts and functions in the ODAS MATLAB Library for extracting information out of mission files and placing it into a hotel file.
The hotel file is ingested by odas_p2mat and interpolated on to the time vector t_slow in your p-file. The resulting data vectors are saved to the same mat-file as the data vectors produced from the p-files. The most common use of a hotel file is to import speed data from a vehicle when the Rockland instrument is not able to measure the speed itself (such as an AUV equipped with a MicroRider, or a Seaglider equipped with MicroPods). An accurate speed estimate is required to convert shear probe data into physical units and to compute gradients of temperature and conductivity. Other data of interest measured by the controller in a vehicle include CT data, pressure, pitch, roll and heading, for example.
If you would like to processes your data without a hotel file, please indicate a reasonable constant speed in meters per second. For example: odas_p2mat(‘file_name.P’,’constant_speed’,1.2)
For more information and an example of Hotel File setup, please review Section 10 of Technical Note 39.
If you are interested in learning more about Hotel Files, please join us for our annual Ocean Microstructure Glider Workshop (OMG Workshop).