Whiskbroom Scanning Pushbroom Scanning

Whiskbroom Scanning:

Whiskbroom scanning is a method of remote sensing where a single detector observes a narrow strip on the ground as a scanning mirror sweeps back and forth. The process is somewhat analogous to how a person might sweep a broom back and forth across the floor. In this scanning technique:

1. Mirror Movement: A scanning mirror is physically moved, often by mechanical means, to redirect the incoming electromagnetic radiation. As the mirror moves, it reflects the radiation from different ground locations toward the single detector.

2. Single Detector: There is only one detector in the system that captures the reflected radiation at any given time. The detector measures the intensity of the radiation for each location as the mirror sweeps across.

3. Strip Imaging: The result is a series of measurements that correspond to a narrow strip of the Earth's surface. As the mirror continues to sweep, the detector captures data from adjacent strips, building up an image of the target area strip by strip.

Whiskbroom scanning is known for its simplicity and ease of implementation. However, it can take longer to cover a wide area compared to other scanning methods like pushbroom. Also, it's important to account for potential distortions in the final image due to the time delay between measurements at different locations.

Pushbroom Scanning:

Pushbroom scanning is another method used in remote sensing, but it involves an array of detectors instead of a single detector. Here's how it works:

1. Array of Detectors: In a pushbroom system, an array of detectors is used, with each detector observing a specific ground location. These detectors are aligned in a row perpendicular to the direction of the scan.

2. Continuous Data Collection: Instead of moving a single detector, a mirror or satellite platform moves the entire array of detectors across the scene. As the mirror/platform progresses, each detector continuously collects data from its designated location.

3. Continuous Strip Image: The result is a continuous strip of data collected over time as the array moves. This strip builds up an image of the target area without the need for multiple sweeps like in whiskbroom scanning.

Pushbroom scanning offers advantages in terms of efficiency and speed when covering large areas. It provides continuous and high-resolution imagery, making it suitable for applications where timely data acquisition is crucial.

Both whiskbroom and pushbroom scanning have their strengths and weaknesses, and the choice between them depends on factors such as the sensor's capabilities, mission requirements, and the desired spatial coverage.

Comments

Thermal Infrared Remote Sensing

1. Principles Thermal Infrared Remote Sensing is based on the detection of naturally emitted electromagnetic radiation from objects, rather than reflected solar energy. According to Planck's Radiation Law , all objects with a temperature above absolute zero (0 K) emit electromagnetic radiation. For Earth surface features, the peak emission lies in the Thermal Infrared (TIR) region of 3–14 μm of the electromagnetic spectrum. The amount of radiation emitted is primarily a function of surface temperature and emissivity . Sensors measure the radiant energy flux density (W/m²) , which is later converted to surface temperature using Stefan-Boltzmann's Law . 2. Radiation Properties in TIR Emissivity (ε): Ratio of radiation emitted by a surface to that emitted by a perfect blackbody at the same temperature. Natural surfaces like water (ε ≈ 0.98) have high emissivity, while bare soils and metals have lower values. Blackbody: An idealized object th...

Atmospheric Window

The atmospheric window in remote sensing refers to specific wavelength ranges within the electromagnetic spectrum that can pass through the Earth's atmosphere relatively unimpeded. These windows are crucial for remote sensing applications because they allow us to observe the Earth's surface and atmosphere without significant interference from the atmosphere's constituents. Key facts and concepts about atmospheric windows: Visible and Near-Infrared (VNIR) window: This window encompasses wavelengths from approximately 0. 4 to 1. 0 micrometers. It is ideal for observing vegetation, water bodies, and land cover types. Shortwave Infrared (SWIR) window: This window covers wavelengths from approximately 1. 0 to 3. 0 micrometers. It is particularly useful for detecting minerals, water content, and vegetation health. Mid-Infrared (MIR) window: This window spans wavelengths from approximately 3. 0 to 8. 0 micrometers. It is valuable for identifying various materials, incl...

Radar Remote Sensing SAR

1. Radar and Radar Remote Sensing RADAR stands for Radio Detection and Ranging . It is an active remote sensing system that transmits microwave energy toward the Earth's surface and records the energy that is returned to the sensor as an echo or backscatter . Unlike passive optical remote sensing, radar does not depend on sunlight. Therefore, it can operate day and night and, at suitable wavelengths, can acquire data through clouds, haze and light rain. Hence, radar is widely described as an all-weather, day-and-night remote sensing technology . Basic principle Microwave pulse → transmission → interaction with surface → backscatter/echo → antenna receives signal → signal processing → radar image 2. Microwave Energy Radar systems use microwave electromagnetic radiation , generally in wavelength ranges from approximately 1 mm to 1 m . Important radar bands include: Band Approx. wavelength Common applications ...

Radar image. Polarization in Remote Sensing

L band radars operate on a wavelength of 15-30 cm and a frequency of 1-2 GHz. L band radars are mostly used for clear air turbulence studies. S band radars operate on a wavelength of 8-15 cm and a frequency of 2-4 GHz. Because of the wavelength and frequency, S band radars are not easily attenuated. . Polarization refers to the direction of travel of an electromagnetic wave vector's tip: vertical (up and down), horizontal (left to right), or circular (rotating in a constant plane left or right). . a synthetic aperture radar (SAR) for high-resolution imaging. a radar altimeter, to measure the ocean topography. echo amplitude a wind scatterometer to measure wind speed and direction. Other types of radars have been flown for Earth observation missions: precipitation radars such as the Tropical Rainfall Measuring Mission, or cloud radars like the one used on Cloudsat. . RISAT-1 (SAR, ISRO India, 2012) RORSAT (SAR, Soviet Union, 1967-1988) Seasat (SAR, altimeter, scatterometer, US, 19...

Discrete Detectors and Scanning mirrors Across the track scanner Whisk broom scanner.

Multispectral Imaging Using Discrete Detectors and Scanning Mirrors (Across-Track Scanner or Whisk Broom Scanner) Multispectral Imaging: This technique involves capturing images of the Earth's surface using multiple sensors that are sensitive to different wavelengths of electromagnetic radiation. This allows for the identification of various features and materials based on their spectral signatures. Discrete Detectors: These are individual sensors that are arranged in a linear or array configuration. Each detector is responsible for measuring the radiation within a specific wavelength band. Scanning Mirrors: These are optical components that are used to deflect the incoming radiation onto the discrete detectors. By moving the mirrors, the sensor can scan across the scene, capturing data from different points. Across-Track Scanner or Whisk Broom Scanner: This refers to the scanning mechanism where the mirror moves perpendicular to the direction of flight. This allows for t...

Vineesh V, Geography

Search This Blog