Hyperspectral Remote Sensing
Hyperspectral remote sensing is also considered imaging spectrometry or imaging spectroscopy. Hyperspectral remote sensing detector system records hundreds of special brands of relatively narrow bandwidths simultaneously. In Multispectral remote sensing, the bands are in discrete form, but in Hyperspectral remote sensing, the bands are continuous. The hyperspectral image analysis technique is derived using the field of spectroscopy which relates to the molecular composition of a particular material, with respect to the corresponding absorption and reflection pattern of light at individual wavelengths.
Digital Image vs Digital Photograph
Photographs are also called snapshots because they are taken in few seconds by exposing a film through a camera and lens, whereas a digital image is not a snapshot, as it scans line by line. An image is a pictorial representation of an object or a scene. Images can be analog or digital images. Analog images are sometimes called photographs. A digital image is produced by electro-optical sensors, composed of tiny equal-sized square picture elements arranged in a two-dimensional matrix. A digital photograph is taken within seconds, whereas a satellite image is recorded line-by-line and may take several minutes. Normalised Difference Vegetation Index
Normalised Difference Vegetation Index (NDVI) is used to map global primary production and is computed as:
(Near-infrared band – Red band) / (Near-infrared band + Red band).
NDVI measures the chlorophyll content of vegetation. Healthy vegetation will have the maximum reflection in the near-infrared part of the electromagnetic spectrum while a vegetation with lack of chlorophyll content or less chlorophyll content will have more reflection in the red (Visible light) part of the electromagnetic spectrum. The main drawback of NDVI is that it is sensitive to the effects of soil, atmosphere, and leaf canopy shadow. Also, in dense vegetation, it quickly reaches saturation.
Active Microwave Remote Sensing - Introduction In Active Microwave Remote Sensing, the energy or pulses are sent by the sensor towards the surface of the earth and then the sensor collects and records the back-scattering. Active Microwave Remote Sensing are mainly of two types: Imaging and non-imaging. The most common form of imaging active microwave sensors is RADAR (Radio Detection and Ranging) A RADAR is essentially a ranging or distance measuring device. It consists fundamentally of a transmitter, receiver, antenna, and an electronic system to process and record the data.
Active Microwave Remote Sensing - Application
A slant range distortion occurs because a RADAR is measuring the distance to the ground object in the slant range rather than the true horizontal distance along the ground. The slant range distortions are Foreshortening | Layover | Shadowing. A Synthetic Aperture Radar (SAR) is a coherent side-looking airborne system that utilizes the flight path of an aircraft to simulate an extremely large antenna or aperture electronically and generate high-resolution remote sensing images. Real Aperture Radar uses an antenna of the maximum practical length to produce a narrow angular beamwidth in the azimuth direction.
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