How satellite measurement can predict the start of the pollen season.
Satellites are normally used for used for three things: communication, taking images and using laser to measure the conditions on earth. But is it possible to use satellites to predict and monitor the development of pollen levels in the atmosphere?
By measuring how light is spread in the atmosphere, satellites can measure the number of particles in the air. However, pollen is hard to detect in this manner. This is partly because pollen reflect light poorly, and partly because pollen is easily confused with other particles. So this approach is not well suited for measuring the number of pollen grains in the atmosphere.
But where satellite measurements come into play is to predict the start of the pollen season. The onset of the pollen season is related to the growth of leaves, e.g. when the leaves have reached a certain development, the plants start to emit pollen.
Vegetation index – chlorophyll levels as seen from space
Satellites can be used to measure the number of leaves that have sprouted by measuring the light reflected by chlorophyll in the leaves. This is illustrated in the video below, which shows the amount of light reflected by chlorophyll over Northern Europe. The images in the video are not generated from photographies taken by satellites, but generated from measurements taken by a spectrometer in satellites. The green color in the video shows the level of the so-called NDVI-index, or vegetation index. Deeper green means a higher value of the NDVI-index.
What does this tell us about pollen levels?
But how can this be used to predict pollen levels? Several studies have shown that there is a correlation between the level of the NDVI-index and the onset of the pollen season. It is not sufficient that the NDVI is above zero, e.g. the start of greening; it has to reach certain levels before the pollen season starts.
Hence, the most obvious use of satellites services with regard to pollen is not the measurements of pollen grains in atmosphere or images of foliage, but rather the measurement of how much light that is absorbed by chlorophyll.
In our previous post about pollen in Europe, we estimate the pollen spread by using on-ground monitoring as basis. We at Airmine are combining the NDVI-index with the on-ground monitoring of pollen and weather data in our pollen forecasting models. We aim to give you detailed forecasts for the onset of the pollen season for birch in Europe, stay with us to be informed!