Jan O. Mattsson

Studies on eolian dust in Greece

The origin of the Mediterranian terra rossa soils is disputed. The current opinion is that these soils are a product of limestone weathering. However, some scientists believe that terra rossa is an eolian deposit originating from North Africa. Our project was inspired by this discussion and deals with eolian deposits and dust storms in Greece. Statistics on episodes with atmospheric dust were extracted from meteorological data taken at a number of Greek weather stations. In addition eolian dust of probably Saharan origin was collected in a number of traps placed by us at weather stations in Crete. Data from the statistics and from the traps are presented, analysed and discussed in this paper.

Planning ‐ topography and climate

The presentation of local climatic data has wide‐reaching effects for planners, designers and those living and working in an area, report Sven Lindqvist and Jan O. Mattsson of the Department of Geography at the University of Lund.

Retroreflection of light from drop-covered surfaces and an image-producing device for registration of this light

Drop-covered surfaces in the landscape such as dew covers cause increased reflection of the incident light in a direction towards the light source, so-called retroreflection. Surveyable registration in the form of imagery of retroreflected light from ground surface and vegetation, for instance from an airplane, may provide valuable climatological and biological information. Different factors influencing the retroreflection are treated in the paper. Among these the lenseffect of the drops is dealt with in detail, and goniophotometric experiments with laser light are mentioned. An active remote-sensing system for registration of retroreflected light from drop-covered surfaces is described. The system consists of a laser scanner equipped with an image-producing device. Laboratory tests with the apparatus are presented as well as planned activities with the equipment.

Tabletop divergent-light halos

We study artificial halos generated by microscopic crystals suspended in an aqueous solution which is illuminated by a divergent light source. By measuring the diameters of the halos we can deduct the refracting angles of the crystals and compare them with known values.

Photography and temperature measurements from a remotely piloted vehicle

Radio-controlled model planes are useful when carrying out photography, especially from low altitudes, and meteorological soundings (air temperatures in boundary layers). Soundings were carried out with a system which stored the measured data on board the plane pending evaluation after the flight. The payload of the plane was a camera and equipment for measuring temperature and air pressure (altitude). Data were stored so that the signals from the temperature and pressure sensors (thermistor and micro aneroid respectively) lit a combination of light-emitting diodes (BCD code) that corresponded to the actual temperature and pressure (altitude). At the instant of measurement, this combination was photographed togther with the ground surface. the camera manoeuvred by means of servo-function. The position of the plane at the instant of measurement was determined on the basis of pressure values and air photographs. Photography from model planes is not a new method. However, previous results have in general been inadequate because, for safetys sake, cheap and consequently less advanced cameras were used. The determination of temperature and other soundings from such aircraft has been little tried hitherto. Photography and sounding from model planes can be of interest in ecological, physical-geographical and meteorological contexts. The method lends itself best to a rapid and handy documentation from the air of a water or land area, e.g. a severely polluted area, or a wind-eroded ground surface, or to the sounding or sampling of aif qualities such as pollution in the smoke plumes of stacks and other types of discharge, of radioactivity in the air over leaking plants, of temperature and humidity conditions in urban boundary layers and of eolian dust in the air over wind-exposed erosion surfaces in arid areas. Radio-controlled model planes could possibly also be used for dissemination of e.g. silver iodide in order to artificially release precipitation and for pollination of forest. (Less)

Improved algorithm for simulations of divergent-light halos

Divergent-light halos are produced when light from nearby light sources is scattered by ice crystals in the atmosphere. We present a theory of divergent-light halos leading to an improved algorithm for the simulation of such halos. Contrary to the algorithm that we presented earlier for simulating such halos, the new algorithm includes a mathematically rigorous weighting of the events. The computer implementation is very compact, and the whole procedure is elegant and conceptually easy to understand. We also present a new simulation atlas showing halos produced by crystals of different shapes and orientations for a set of elevations of the light source.

Heiligenschein and related phenomena in divergent light

When seen in divergent light, atmospheric optical phenomena could appear to be modified. We describe some geometric and retroreflectional effects of light divergence on heiligenschein and related phenomena that, to our knowledge, have not been previously reported. These geometric effects are compared with and set in relation to the geometric effects on other atmospheric optical phenomena.