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The CRS concept will also be applied to temporal domain when applicable. One local time frame that is useful for defining the geometry and dynamics of scanners is seconds
past the start of a scan scan start time. Also, for some sensor systems, time is recorded relative to a local clock or the start of the mission. In such cases, time frames and their
relationship to “Earth time” will be defined in SensorML.
7.6 Measurement observation concepts
A sensor is designed to measure a particular property within a given sample space. When these measurements are taken, they result in an observation that may be immediately
utilized or stored. In its lowest level, this observation is typically a proxy measurement of some property other than the desired physical property, itself. For example, an
observation may be the height of mercury in a thermometer or the voltage across a circuit. In order for these observations to be related to a more useful physical property, a
new observation will typically be derived using known sensor calibration functions and perhaps other processing algorithms.
SensorML allows one to describe whatever level of observations the creator of the document wishes to expose. For example, one might specify that the sensor measures raw
voltages and then provide calibration descriptions that would allow conversion to other physical quantities. Alternatively, or in addition to, the sensor description might specify
that the sensor measures temperature, and then expose the calibration used to derive those temperature values, or not.
A SensorML document will describe what physical properties are measured by the sensor, as well as information concerning the properties and quality of these
measurements. In addition, a SensorML document may provide or link to the values of these measurements using one or more data provider types. However, a SensorML
document does not typically contain the observation values resulting from the measurement.
7.7 Sensor response characteristics
The response characteristics of a sensor determine how the sensor will react to a particular stimulus i.e., phenomenon and how it will operate under given environmental
conditions. Within the sensor response characteristics will be specifications for sensitivity e.g., threshold, dynamic range, capacity, band width, etc., accuracy and precision, and
behavior under certain environmental conditions.
A very large number of sensor response characteristics can be defined using a general response model e.g., the detector model defined in Annex C. However, there may be
specific sensors that require addition of different parameters to fully describe their response behavior. Where possible, these should be derived from the general model.
7.8 Sample and collection geometry concepts
