Marine Device Data Collection

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This page coordinates the DOWG effort to collect variable-level data on multiple devices: What they measure and what they can output.

Directions for Providing Data

Please follow these directions for providing your data to this collection.

Collected Device Data Report

When it is available, we will post a report on device data collected so far.

What We're Collecting

We are collecting two sets of terms for each submitted device. The first set of terms describes the phenomena that are actually measured by the devices. The second set of terms describes the values that are output by the devices. If this is not transparent, some additional material describing it is below.

An Example: A Classic CTD

An example of the difference is provided by the classical Conductivity-Temperature-Depth sensor. In many cases, this sensor actually measures the parameters conductivity, temperature, and pressure. However, CTDs may report conductivity, temperature, and depth (converting pressure to depth using an approximate equation, or using user-entered parameters for latitude to provide a more precise conversion), or in some cases, salinity, temperature, and depth.

The input, or measured, variables in this case would be conductivity, temperature, and pressure.

The output, or reported, variables are conductivity, temperature and depth; or salinity, temperature, and depth, as appropriate.

Discussion: Details of Measurement Models

Probably this is the best/easiest model diagram. In this diagram, a real-world Phenomena (sic) has a real-world Property like its "depth relative to sea level". This property is directly an Observable in this case. The Instrument is a device that can measure this Observable, thereby producing a Measurement (not shown). This provides some basic terminology for us to use.

To more precisely show the transformation from the real world to measurements, let's use some drawings illustrating the SensorML model. This simple I/O drawing from Mike Botts shows a simple relationship between the external world and a measurement. In this cartoon, a sensor transforms the external realities of temperature and pressure, T(r) and P(r) into measured values, T(m) and P(m), following nice linear relationships -- a perfect measurement! T(r) and P(r) are Properties of the body of water; they are observable. T(m) and P(m) are Measurements. Both may be described using the terms (Water) Temperature and Pressure.

But the real world is more complex, as shown in this more complex I/O diagram. Here the real temperature T(r) turns into a resistance, R, which is then translated into the measured temperature, T(m). Likewise, pressure goes through a volts value V.

So in this second case, which is more like a real sensor, we still have the inputs and outputs of temperature and pressure. But we *also* may have outputs of 'resistance (from temperature)' and 'voltage (from pressure)'. These are direct Measurements, just like the T(m) and P(m).

And for another variant, consider a CTD device that *only* reports the temperature, salinity and depth, even though it is measuring the conductivity, temperature, and pressure. Although the salinity Property is determined, there is no direct measurement of salinity. Instead, a true model would show measurements of conductivity, temperature, and pressure (and perhaps an input of latitude), and outputs of temperature, depth, and salinity. Here there is very little overlap between the measurements being taken and the outputs being presented.

For our purposes, the first list should be the input Observable Properties -- temperature, conductivity, and pressure. The second list should be the output 'measurements', however they may be derived -- temperature, depth, and salinity. In many cases the same variable may appear in both lists, but this depends on the technological implementation.

Analysis of Data

Most of the key data has been collected into an Excel spreadsheet. This worksheet contains all the vocabularies submitted so far. Some metadata about the organization and the like is missing, but it can be obtained from the emails later. The main concern here is about having the ID of the sensor and the related parameters. Note that we usually cannot say if parameters were input or output.