TherMap - Thermal Maps for topographically determined regions

TherMap version 1.06© - released 01.04.2010

On August 6, 2008, on the occasion of the Opening of the Gliding World Championships at Lüsse/Berlin, Germany, OSTIV awarded Dr. Beda Sigrist a diploma for this innovation, considered the work to be " a quantum leap in analizing and optimizing flight paths in known and unknown orographies". The utilization of these maps for non-commercial purposes remains free. For commercial uses, quotations, as well for further publication written copyright permission must be obtained via the mail address mentioned at the end of this site, and this site quoted as the source.

Thermal maps for
mountain regions

For ridge wind maps
see WindMap

Français - Deutsch

Welcome to TherMap

Position the cursor on the picture on the left and you can see a map extract of TherMap, a tool for glider pilots, to visualize the local potential of thermals on digital maps on a given date and hour, assuming no meteorological interferences. For any sensible time and date of interest, thermal hotspot maps can be downloaded from this site. As an alternative, complete sets of country maps for Switzerland, Austria, the French Alps, the Pyrenees as well as the Northern and Central Apennine can be ordered on CDs at a cost covering charge.

Before the flights TherMap maps allow you to study the best itineraries, or to explain them to less experienced pilots, particularly across less known regions. After the flight, you may superimpose your flight tracks on these maps, typically IGC-files, to find out where you might have followed more promising paths. The maps may also be imported as raster maps into certain flight analysis applications.

What is new in TherMap 1.06
To facilitate the reading texts and gridlines are now displayed in combined black and white. The colouring of the upwind areas has however remained unchanged, having found no valid alternatives despite intensive research. An important extension is however the new possibility to automatically overlay the maps on Google Earth, where they can be visualized as 3D-displays as well as in 3D flight simulations.

Click on what you want to see

The TherMap Model

a. Irradiance maps
b. Temperature maps
c. Thermal pressure maps
d. Slope maps

a. Irradiance Maps

Digital elevation models (DEM), such as the worldwide 90m SRTM satellite models, provide a relatively detailed topographical profile of the surface of the earth. Extracts of these files can be used to determine the vertically projected irradiance of each raster field on a given date and daytime, which can then be visualized on corresponding irradiance maps.

Thermals are part of the atmospheric energy flow caused by this solar irradiation. The results have shown that irradiance maps can be used to predict where thermals are likely to occur, particularly during the morning hours of Alpine regions.

Irradiance maps, however, show an instant situation, whereas heating up the surface and the air causing the thermals takes time. This becomes evident during the afternoon hours. The answer to this are temperature maps expressing how much heat has been accumulated at a given place and time.

Region of Aletsch glacier on June 20, 10.00h UTC: The intensities are from green via yellow to red.
The white spots are expected thermal takeoff points

b. Temperature Maps

For practical reasons TherMap computes the heat accumulation at the surface using a relatively simple empirical smoothing algorithm, to approximate the evolution of the surface temperature at the usual flight altitudes. To simulate the effect of the actual orography Thermap considers the cooling effect of calculated forest areas and seasonal vegetation, and makes an approximation for the Albedo effect of snow and permafrost surfaces. With these adjustments the resulting temperature maps are plausible predictors of the location of thermals during the afternoon hours.

To validate and refine the maps, IGC-flight tracks have been superimposed, using colour codes to distinguish between climbing and descending flight phases. This way the agreement between the hotspots and their influence on the flights could be visualized. The map extract shown below, of a flight across the Aletsch glacier region, illustrates that the climbing phases coincide very well with the yellow/red hotspots.

Temperature map of Aletsch glacier region on June 28, 12.00h UTC.
Note the high level of agreement with the superimposed flight path (blue = climbing, white = sinking)

In his publications the German glider pioneer Jochen von Kalckreuth mentioned that thermals on slopes exceeding about 25 to 30 degrees tend to climb along the slope until they reach a smaller slope or an edge. TherMap also considers the snow and permafrost limits, where thermals climbing along the slope meet the cold air coming from above, an additional reason causing thermals to take off.

c. Thermap Pressure Maps

Irradiance and temperature maps basically show evenly distributed irradiance or temperatures across mountain sides with constant orientation and slope. During hot afternoon hours the maps therefore tend to be overloaded with hot spots and too blurred for our purposes. This problem also persists if all but the hottest spots are masked out. With the thermal pressure maps, TherMap could finally overcome these weaknesses.

The idea of the thermal pressure is based on the insight that any air "bubble" heated above a slope develops a lift force which can be decomposed into two components, namely one along the line of steepest ascent of the slope, and one perpendicaular to the slope. The first one creates a pressure along the line of steepest ascent. This pressure is basically distributed proportional to the slope angle, but diminishing slowly with the distance from the original bubble, until the residual pressure falls below a critical value or until a takeoff point is reached. The initial lift of the bubbles is derived from the temperature maps, from which the thermal pressure maps can then be derived in an additional computation run based on the principles just described.

The resulting thermal pressure maps are more precise to visualize the local potential for thermals. The following picture illustrates that thermal pressure maps even provide detailed results for southward facing slopes on hot summer afternoons.

Thermal pressure map of June 28, 12h UTC, with the same flight track. The thermal hotspots are shown far more precisely than on the corresponding temperature map, as one can see by moving the cursor on the image in order to see the original map.

d. Slope Maps

Slope angles and mountain ridges have s significant influence on the thermal activities. TherMap therefore also shows slope maps facilitating the overview of a region. The colouring of the map is simply determined by the slope angle.

Using the Maps

a. Selecting the right maps
b. Limitations of radar satellite maps
c. How to read the maps
d. Preflight use of maps
e. Post-flight analysis using the maps

a. Selecting the right maps

Country :

Depending on the extent of your flight you may have to select the maps of more than one country or region

Country/Region	North-West Corner	South-East Corner
Switzerland	48° 00'’ N / 05° 30’ E	45° 30'’ N / 11° 00’ E
Austria	48° 00'’ N / 09° 30’ E	46° 00'’ N / 16° 20’ E
French Alps	47° 30'’ N / 05° 00’ E	43° 12'’ N / 07° 30’ E
Pyrenees	43° 20'’ N / 03° 00’ W	42° 00'’ N / 02° 30’ E
Northern Apennine	45° 00'’ N / 07° 30’ E	43° 30'’ N / 12° 30’ E
Central Apennine	43° 30'’ N / 11° 30’ E	41° 00'’ N / 15° 00’ E

Date :

TherMap provides maps of selected dates from the beginning of April to the middle of September (Months 4 to 9). Select the maps showing the date closest to the flight date.
The map date is included in its name (month-day)

Time:

UTC is now generally used, wherby 3 map times per day have been included in the map collection, namely one for the latest full hour before the highest elevation of the sun, and two others 3 and 6 hours later, respectively. If we tolerate that the map-time may differ up to 90 minutes from the flight, these three maps basically cover a core flight interval of about 8 hours.

UTC is normally also used in the flight records. Select the map closest to the time of overflight. A longer flight will therefore require several maps. This also applies to flight analyses, for which TherMap maps are typically imported as raster maps into flight analysis tools in order to visualize on them the flight track.

b. Limitations of TherMap approach

Accessing the internet through a high speed line is not always possible. It may then be simpler to access the maps directly on a CD. Corresponding map sets are therefore delivered against pre-payment in Switzerland and the EU . For this purpose you can send TherMap an order by E-mail with the following indications:

Who is behind TherMap ?

TherMap is a private initiative of Beda Sigrist, a senior Swiss glider pilot with a solid background in engineering and computing. Impressed by the precision of the regional meteorological forecasting tools of RegTherm and TopTherm, he started to investigate the possibilities of making use of presently available topographic data, along the ideas of TherMap. With the primary advice of Olivier Liechti, the initiator of Regtherm and Toptherm, the encouragement of OSTIV, particularly of Hermann Trimmel, as well as the positive response of numerous experienced glider pilots, he pursued the development of TherMap up to the present version. The flying club of Gruyère has been hosting the site from the beginning. The feedback by pilots and experts has permitted to continuously improve the model and to update this site with still better maps. In this respect particular thanks go to Alfred Ultsch, for his additional validations on the basis of flightlogs, his publication of the findings (ref. 10), and for his pertinent improvement proposals. Special thanks go to Iakov Shrage, a top competition glider pilot besides 21500 hours as an airline pilot, who encouraged the extension of this site to also cover the region of Slovakia.

Can the application behind TherMap be purchased?
No, it cannot. It would of course be interesting to have available directly the source code needed to generate the maps. TherMap is however still a young project and further improvements as well as enhancements are likely. If the source code was distributed, the product would have to be wrapped up as a professional package and update management procedures introduced to ensure that the users would always have available the latest version. The resulting costs would require a commercial approach. Apart from the much bigger effort, this would be in conflict with the conditions set by SRTM, the distributor of the satellite data, which is basically only made available for non-commercial use.

What possibilities exist to use the TherMap model for topographically smoother regions ?
This is a question we continue to ask ourselves. With the introduction of the thermal pressure model it has now also become possible to produce maps for regions outside the mountains, such as the Jura. In topographically still less pronounced regions the local variations of the surface becomes smaller and more diffuse, making it more difficult to identify topographically induced thermal takeoff areas. In addition the flight level above ground are usually higher than in mountain areas, making it also more difficult to validate possible thermal models on the basis of flight track data. However thermals always have a physical cause. It may therefore be possible that other than topographic causes, such as the infrared characteristics of the surface, may some day also become freely available and permit to develop solutions for flatter regions.

What possibilities exist to generate TherMap images reflecting the actual local wind conditions at a given time?
This question can probably only be answered in the longer term. In Europe diagrams showing the hourly meteorological evolution are available for regions of 50 to 100 kilometers. On this basis in would, in principle, be possible to generate corresponding TherMap presentations. The data would however have to be paid, because it would have to be supplied in automatically processible formats. In addition there would also be the costs for making available the TherMap results every day, whereby it is not sure whether there would actually be a sufficient demand for such detailed information. The future will have to decide this.