OBJECTIVE FORESTRY

Detailed explanation-1: -There are two types of remote sensing instruments-passive and active. Passive instruments detect natural energy that is reflected or emitted from the observed scene. Passive instruments sense only radiation emitted by the object being viewed or reflected by the object from a source other than the instrument.

Detailed explanation-2: -Remote sensing systems which measure energy that is naturally available are called passive sensors. Passive sensors can only be used to detect energy when the naturally occurring energy is available. For all reflected energy, this can only take place during the time when the sun is illuminating the Earth.

Detailed explanation-3: -Sensors can be classified into two main categories: active and passive. Active sensors emit energy and measure the reflected or scattered signal, while passive sensors detect the natural radiation or emission from the target or the environment.