Lessons and Modules
Introduction to Clouds
Studying Clouds from Space
From their positions high in orbit above the earth, satellites offer an ideal means of observing large scale events, including storms, as they occur on the earth. You already have an idea of how large storm systems appear from viewing the satellite images of storm clouds used by weather forecasters on television. How are these images created?
Satellite Data Collection
An animated illustration of a satellite with both passive and active instruments is shown below. The active instruments emit electromagnetic waves down to the earth. The satellite then retrieves these waves as they are reflected to see how they have changed. The passive instruments on the satellite only observe solar radiation reflected by the earth or other electromagnetic waves originating from the earth.
|A satellite receiving information via solar light reflected by the earth.|
A closer view of a satellite collecting data is shown below. Solar light travelling through space hits the earth's surface at various positions. The red boxes indicate grid lines that enable scientists to determine the location of a given position. These grid lines are for mathematical purposes only and do not exist in reality. The solar light is then reflected upwards by different amounts depending upon conditions at the surface at those positions at a given time. In space, the satellite receives the reflected solar light and heat radiation from the earth. Sensors on the satellite detect these parameters and their values are recorded to be sent back to the earth.
In the illustration above, the satellite could for example, be retrieving data pertaining to cloud properties. The next stage involves converting information received by the satellite instruments into meaningful data. How is satellite data produced?
Satellite Data Processing
An illustration of the process of acquiring satellite data is provided below. After sensors on the satellite detect the amount of solar light reflected and the heat radiated from the earth, an on-board computer interprets the information into numerical values and stores them for transmission back to the earth.
The satellite travels along its orbital path around the earth, collecting and storing data. When it passes over its land-based receiving antenna (once every orbit), the satellite transmits the data collected back to earth. This data is then fed to more powerful computers, interpreted, and gridded accordingly. The next section describes the process of going from satellite data to images of clouds.