Watershed. Catchment. Basin

A watershed, also known as a river basin or drainage basin, is a fundamental concept in geohydrology and hydrology. It refers to a specific geographic area or region of land where all the surface water, including rainfall, snowmelt, and runoff, drains into a common outlet, such as a river, lake, or ocean. Here's an explanation of each term:

1. Watershed: A watershed is essentially a natural hydrological unit defined by the topography of the land. It represents the entire area from which all precipitation and surface water flow eventually gathers at a single point. This point is typically where the main river or stream within the watershed exits into a larger body of water, such as an ocean. Watersheds come in various sizes, from small ones that encompass a few square miles to enormous ones that cover entire continents.

2. River/Drainage Basin: A river basin or drainage basin is another way to describe a watershed. It's the land area that collects and channels water into a river and its tributaries. A river basin is made up of the river itself and all the contributing streams, creeks, and smaller waterways within that watershed. These smaller watercourses merge into the main river, which eventually flows into an ocean, sea, or a larger river. River basins can be quite extensive and are the fundamental building blocks of the planet's hydrological cycle.

3. Catchment Area: The catchment area is a term often used interchangeably with watershed, particularly in the context of smaller, localized areas. It represents the land that catches and collects rainfall, allowing it to flow into nearby rivers or streams. This area defines the boundaries within which precipitation contributes to the water supply of a particular river or water body. A catchment area is essentially a subset of a larger river basin, encompassing the specific area where a particular river's water sources originate.

In summary, these terms are all related to the movement of water on the Earth's surface. A watershed, river basin, and catchment area define the geographical boundaries where surface water collects and eventually drains into a common outlet, forming the basis of the Earth's complex water systems and hydrological processes.

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Platforms in Remote Sensing

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In Remote Sensing , satellites record electromagnetic radiation (EMR) that is reflected or emitted from the Earth. Before reaching the sensor, radiation interacts with: The Atmosphere The Earth's Surface These interactions control how satellite images look and how we interpret them. I. Interaction of EMR with the Atmosphere When solar radiation travels from the Sun to the Earth, four main processes occur: 1. Absorption Definition: Absorption occurs when atmospheric gases absorb radiation at specific wavelengths and convert it into heat. Main absorbing gases: Ozone (O₃) → absorbs Ultraviolet (UV) Carbon dioxide (CO₂) → absorbs Thermal Infrared Water vapour (H₂O) → absorbs Infrared Concept: Atmospheric Windows These are wavelength regions where absorption is very low, allowing radiation to pass through the atmosphere. Remote sensing depends on these windows. For example, satellites like Landsat 8 use visible, near-infrared, and thermal bands located in atmospheric windows. 2. Trans...

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