Geoscience Reference
In-Depth Information
quality and homogenity, which makes the results uncertain regarding input data, in
addition to the uncertainty of the approach. Quantifying quality and homogenity of
the data require data about the data itself (the metadata). Nowadays, metadata are
highly standardized for GI data (e.g. see the Open GIS Consortium activities), but
the information obtained from metadata regarding climate data is still heterogenous.
However, the NMSs and the WMO (World Meteorological Organization) are aware
of the importance of climate metadata, which resulted in several efforts for
standardization of metadata (see e.g. [AGU 03]). To summarize these efforts, it can
be stated that in climatology metadata information is related to the documentation of
the “where”, “when”, and “how” of measurements, whereas metadata in GI science
also add emphasis to the usability of the data.
In this chapter, basic concepts of climate networks and climate data are
presented. This includes an overview of standards of climate measurements,
description of climate data types, spatial reference of data, as well general comments
on accessing the data. The areas of climate data quality and homogenity are
reviewed in depth, covering the important aspects of metadata description. The
chapter does not tackle climate model data and only introduces climate reanalysis
data.
1.1. Data measurements and observations in climatology
1.1.1.
Networks and concepts for meteorological/climate data
Meteorological measurements are motivated by the primary aim of predicting the
Earth's weather with the highest possible precision. This aim results in
measurements covering the entire Earth (for both the land and the sea), but also
encompassing the third dimension (vertical sounding of the atmosphere by radio
sounds, satellite sensors, radar, etc). Beside weather forecasting, meteorological
services are responsible for monitoring the state and spatiotemporal change of the
climate. As these two basic aims do not coincide with respect to network
performance, two different networks have been established in public weather
services, the synoptic and the climate network. Whereas, the stations and
instruments are identical, the networks differ in their interval, quantity, availability
and time of observations. Moreover, the synoptic network is characterized by the
need for a much larger spatial extent and more detailed information on past and
current weather situations. In contrast, climate networks are characterized by higher
demands on data quality. All national meteorological/climatological networks are
coordinated on an international level by the WMO.
The need for meteorological/climatological networks is met by
in situ
measurements and by remote sensing techniques. Consequently, the WMO Global
Observing System is composed of the surface-based subsystem and the space-based
subsystem. The surface-based subsystem includes different types of station
networks (e.g. surface synoptic stations, climatological stations), whereas the space-
based subsystem comprises, for example, on-board sounding from spacecraft. The
