tailieunhanh - Biomass and Remote Sensing of Biomass Part 8

Tham khảo tài liệu 'biomass and remote sensing of biomass part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Introduction to Remote Sensing of Biomass 131 their own source of energy an example would be a radar gun. These sensors send out a signal and measure the amount reflected back. Active sensors are more controlled because they do not depend upon varying illumination conditions. Passive sensors Fig. 2. Active and passive sensors Active sensors Orbits and swaths The path followed by a satellite is referred to as its orbit. Satellites which view the same portion of the earth s surface at all times have geostationary orbits. Weather and communication satellites commonly have these types of orbits. Many satellites are designed to follow a north south orbit which in conjunction with the earth s rotation west-east allows them to cover most of the earth s surface over a period of time. These are Near-polar orbits. Many of these satellites orbits are also Sun-synchronous such that they cover each area of the world at a constant local time of day. Near polar orbits also means that the satellite travels northward on one side of the earth and the southward on the second half of its orbit. These are called Ascending and Descending passes. As a satellite revolves around the earth the sensor sees a certain portion of the earth s surface. The area imaged is referred to as the Swath. The surface directly below the satellite is called the Nadir point. Steerable sensors on satellites can view an area off nadir before and after the orbits passes over a target. Satellite sensor characteristics The basic functions of most satellite sensors are to collect information about the reflected radiation along a pathway also known as the field of view FOV as the satellite orbits the Earth. The smallest area of ground that is sampled is called the instantaneous field of view IFOV . The IFOV is also described as the pixel size of the sensor. This sampling or measurement occurs in one or many spectral bands of the EM spectrum. The data collected by each satellite sensor can be described