A large number of direct in-situ hydrological observations are performed by a sensor or sensor system. Common types of sensors include rain gauges, level gauges, quality sensors such as temperature, turbidity etc. <br /></p><p>Manual procedures may be also used to make measurements at a particular sampling point. These may be ad-hoc visits to particular point that may be of interest, or continued visits to a well identified sampling point. <br /></p><p>Procedures that generate derived or synthetic results also exist, such as those produced by algorithms or simulations. Algorithms are commonly implemented in hydrological software to process data sets for reporting or other purposes. Examples include:<br /></p><p>- Temporal interpolation or aggregation;<br /></p><p>- Spatial interpolation;<br /></p><p>- Quality assurance related tasks such as automatic spike removal or gap filling;<br /></p><p>- Derivation of new observed phenomena such as calculation of volume from stage, discharge (flow) from stage etc.<br /></p>