Test: Remote sensing - Civil Engineering (CE) MCQ

Photons are the main constituent particles in the electromagnetic energy. The relation between velocity, wavelength and frequency is determined as λ = c / f, where λ represents wavelength, f is the frequency of the wave and c represents the velocity of the wave, which is equal to speed of light.

Radiometric Resolution

• The radiometric resolution of an imaging system describes its ability to discriminate very slight differences in energy.
• The finer the radiometric resolution of a sensor, the more sensitive it is to detect small differences in reflected or emitted energy.
• It refers to the sensitivity of sensor to incoming radiance.

Spatial Resolution

• Measurement of the minimum distance between two objects that will allow them to differentiate from one another in an image.
• Spatial resolution of the sensor refers to the size of the smallest possible feature that can be detected.
• Spatial resolution is a measure of smallest object that can be resolved by the sensor, or the size of area on the ground represented by each pixel. Pixel size is used to determine resolution quality.

Spectral Resolution

• Spectral resolution describes the ability of a sensor to define fine wavelength intervals. The finer the spectral resolution, the narrower the wavelength range for a particular channel or band.
• Spectral resolution refers to the specific wavelength intervals in electromagnetic spectrum that a sensor can record.
• Narrow bands have higher spectral resolution.

Temporal Resolution

• Each satellite has its own unique revisit schedule for obtaining image of a particular area.
• The frequency at which the sensor revisits an area is known as temporal resolution.
• For example, if a satellite images the same area every 10 days, then its temporal resolution would be 10 days.
• Temporal resolution is an important factor to consider in change detection studies i.e. crop growth etc.
• Hence, temporal resolution is the amount of time taken by sensor to return to a previously recorded location.
  Examples – Landsat, GOES and NOAA

Electro-magnetic waves are used in case of remote sensing. The different waves present in this spectrum enables us to use a variety of waves based on the condition present and can be able have a better output.

• The Enhanced Thematic Mapper Plus (ETM+) is the main instrument on board Landsat-7 and has been operational since 1999.
• Landsat 7 Enhanced Thematic Mapper Plus (ETM+) images consist of eight spectral bands with a spatial resolution of 30 meters for Bands 1 to 7. The resolution for Band 8 (panchromatic) is 15 meters.
• All bands can collect one of two gain settings (high or low) for increased radiometric sensitivity and dynamic range, while Band 6 collects both high and low gain for all scenes.
• Approximate scene size is 170 km north-south by 183 km east-west (106 mi by 114 mi).

Remote sensing involves certain principles which are applied for having a good result of the desired output. The principles are electromagnetic energy, electro-magnetic spectrum, interaction of energy with atmosphere etc.

Triangulated Irregular Network

• It is set of adjacent, non-overlapping triangles computed from irregularly spaced points.
• Digital TIN data structures are used in a variety of applications, including geographic information systems (GIS), and computer aided design (CAD) for the visual representation of a topographical surface.
• A TIN is a vector-based representation of the physical land surface or sea bottom, made up of irregularly distributed nodes and lines with three-dimensional coordinates (x, y, z) that are arranged in a network of non-overlapping triangles. 
• A TIN used to represent terrain is often called a digital elevation model (DEM), which can be further used to produce digital surface models (DSM) or digital terrain models (DTM). 
• An advantage of using a TIN over a rasterized digital elevation model (DEM) in mapping and analysis is that the points of a TIN are distributed variably based on an algorithm that determines which points are most necessary to create an accurate representation of the terrain

A wide range of waves are present in case of electromagnetic spectrum, off which the gamma-rays are having a nano level wave length capacity i.e., less than 0.03nm.

Types of data used in GIS 
Nominal Data: The only thing a nominal scale does is to say that items being measured have something in common, although this may not be described.
Ordinal Data: Items on an ordinal scale are set into some kind of order by their position on the scale. This may indicate such as temporal position, superiority, etc.
Interval Data: Interval data (also sometimes called integer) is measured along a scale in which each position is equidistant from one another. This allows for the distance between two pairs to be equivalent in some way.
Ratio Data: In a ratio scale, numbers can be compared as multiples of one another. Thus one person can be twice as tall as another person. Important also, the number zero has meaning.
"Interval Data" and "Ratio data" measures quantity hence are Quantitative Data.

Visible region consist of three color waves red, blue and green remaining are the combination of those. The blue light is having a wavelength range of 0.42-0.52 micrometer.

Map Overlay

• It is the process by which it is possible to take two or more thematic map layers of same area and overlay them on the top of other to form a composite new layer.
• Map overlay is an important technique for integrating data derived from various sources and perhaps is the basic key function in GIS data analysis and modeling surfaces.
• This technique is used for the overlay of vector data (for example, pipelines) on a raster background image (often a scanned topographic map) overlays where new spatial data sets are created involving the merger of data from two or more input data layers to create a new output data layer.

Map Projection

• Map projection is a basic principle of map making.
• In this process when projected on to a flat map, objects on the earth's surface are distorted in some way, either in size, shape or in relative location.

Topology

• In GIS, topology is the term used to describe the geometric characteristic of objects which do not change under transformations and are independent of any co- ordinate system.
• Topology may be defined as constituting those properties of geometrical figures that are invariant under continuous deformation.