scope:

Introduction

For aerological measurements (measurement of meteorological Parameters in the free atmosphere), balloons are predominantly used as instrument carriers for radiosondes. The measurement quantities concerning air temperature, humidity, pressure, and, if necessary, the velocity and direction of the wind are transformed by the radiosonde into an electrical Signal, and are transmitted by radio to the ground Station receiver. As free balloons drift with the wind, the wind can be determined at different heights by measuring the flight path of the balloon.

Apart from wind direction and velocity as well as temperature and humidity near the ground, the diffusion of atmospheric pollutants also depends on how these quantities change in correspondance with increasing height above ground (vertical wind, temperature or humidity profile or vertical temperature or humidity gradient, respectively). The width of the vertical ränge depends on what is to be measured.

In general, aerological measurements for questions of air pollution are carried out at heights up to 3000 m above ground. The measured data are representative horizontally within the order of magnitude of some ten kilometers, and, at the lower ränge of the ascent, they depend heavily on orographic conditions.

For air pollution prevention, the following information is frequently used:

- type and frequency of vertical profiles of wind direction and velocity,

- mechanism and vertical width of wind systems which are influenced by orogaphic conditions,

- frequency and duration of inversions as well as their upper and lower limits,

- height of the Inversion in case of smog.

In the following, only the "direct" (in situ) measurement procedures are described where the measuring Instrument is transported to the measurement site by means of a balloon, or the balloon itself serves as a means for the measurement. Indirect or remote sensing, as, e.g., the SODAR and LIDAR methods, are not dealt with in this Guideline.

It is the aim of aerological measurements to determine the vertical distributions of the measurement quantities mentioned above at a fixed site and at a fixed date. Strictly speaking, these conditions on place and time are not met because of the drift of the balloon and the duration of the measurement. For measuring tasks within the frame of this Guideline, however, measurements which are carried out by means of free balloons may be allocated sufficiently enough to a fixed place (launching site) and a fixed time (starting time).

For aerological soundings, it is necessary to measure the air pressure in order to allocate, by means of the barometric height formula, the height of the measured temperatures and humidities, as far as they are not allocated by the determination of the balloon's Position (see Section 1.4.1).