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,

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, 1978)

ERS-1 & ERS-2 (European Remote-Sensing Satellite) (altimeter, combined SAR/scatterometer)

TOPEX/Poseidon (altimeter)

Tropical Rainfall Measuring Mission (Precipitation Radar)

Cloudsat (cloud radar)

Metop (scatterometer)

QuickScat (scatterometer)

Polarization in radar imaging refers to the orientation of the electric field of the radar waves that are used to illuminate the target. There are two main types of polarization: linear and circular. Linear polarization has the electric field oscillating in one plane, while circular polarization has the electric field oscillating in a circular pattern. The type of polarization used can affect the radar image, as different types of targets will reflect the radar waves differently based on the polarization. For example, linear polarization is better for detecting targets with smooth surfaces, while circular polarization is better for detecting targets with rougher surfaces. Additionally, using different types of polarization can help to reduce the effects of interference from other sources.

HH, HV, and VV are types of polarization that are used in radar imaging.

HH stands for horizontally polarized transmitted signal and horizontally polarized received signal. This type of polarization is useful for detecting targets with smooth surfaces, as the horizontally polarized radar waves will be reflected more efficiently by these types of targets.

HV stands for horizontally polarized transmitted signal and vertically polarized received signal. This type of polarization is useful for detecting targets with rougher surfaces, as the horizontally polarized radar waves will be scattered in many directions by these types of targets, resulting in a stronger return signal.

VV stands for vertically polarized transmitted signal and vertically polarized received signal. This type of polarization is useful for detecting targets with rougher surfaces, as the vertically polarized radar waves will be scattered in many directions by these types of targets, resulting in a stronger return signal.

Using these different types of polarization can help to enhance the contrast and details in radar images, and also it can be used to extract information about the targets, such as their shape, size, and surface roughness.

Comments

Regional Geography, Systematic Geography, Idiographic, Nomothetic, Inductive and Deductive Approaches

T wo major ways of studying Geography : the Regional Approach and the Systematic Approach . It also explains the related ideas of idiographic vs. nomothetic and inductive vs. deductive reasoning , especially in the context of the Hartshorne–Schaefer debate . 1. Regional Geography: “All About One” Regional Geography studies one particular region in detail . A region is an area that has some degree of homogeneity (sameness) within its boundary but is also unique or different from other regions . For example, if we study Palakkad District , we may study: Relief and drainage Climate Soil Vegetation Agriculture Population Occupation Economy Culture Political characteristics The purpose is to understand the complete geographical personality of Palakkad and the relationships among its different features. Key concepts Region: A geographical area with identifiable characteristics and boundaries. Homogeneity: Si...

Kuhn’s Paradigms

The given content explains Thomas S. Kuhn’s model of scientific development , its application to geography, and criticisms by Karl Popper, Paul Feyerabend, Michel Foucault , and others. 1. Basic Idea Kuhn argued that science does not develop continuously in a straight line . Instead, scientific development occurs through: Preparadigm → Paradigm → Normal Science → Crisis → Scientific Revolution → New Paradigm A new paradigm may replace an older one, producing a major change in the way scientists understand and study a subject. Concepts and Terminologies Concept / Term Simple Meaning Paradigm A commonly accepted framework/model that guides scientific research Exemplar A successful concrete problem-solution used as a model for future research Disciplinary Matrix Shared beliefs, values, concepts, methods and techniques of a scientific community Preparadig...

Multispectral and Hyperspectral Imaging Systems

The main idea is how a remote-sensing sensor collects information about an area . A sensor does not simply take an ordinary photograph. It measures the electromagnetic energy reflected or emitted by objects in different wavelength bands . Depending on how many bands are measured and how the sensor collects them, different imaging systems are used. 1. Multispectral vs. Hyperspectral Multispectral imaging (MSI) records information in a limited number of relatively broad, separate spectral bands , such as blue, green, red, near-infrared and shortwave infrared. Hyperspectral imaging (HSI) records information in many narrow and usually contiguous spectral bands . Therefore, it provides a much more detailed spectral signature of each pixel. The resulting dataset is commonly called a hyperspectral data cube (hypercube) because it contains: X-axis → spatial information Y-axis → spatial information Z-axis → wavelength/spectral information Thus, hype...

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...

Satalite

Landsat → Land resources SPOT → High-resolution mapping IRS → Indian natural-resource mapping ASTER → Geology + thermal + DEM QuickBird → Very high spatial resolution MODIS → Daily global monitoring GOES → Weather monitoring AVHRR → Weather + vegetation + ocean AVIRIS → Hyperspectral imaging Highest spectral resolution: AVIRIS (224 narrow bands) Highest spatial resolution in this list: QuickBird (~0.61 m PAN) Highest temporal frequency: GOES (minutes) Best broad global monitoring: MODIS Indian sensors: IRS-LISS III and LISS IV Hyperspectral: AVIRIS Thermal + multispectral + DEM: ASTER abbreviations MSS – Multispectral Scanner System TM – Thematic Mapper ETM+ – Enhanced Thematic Mapper Plus GOES – Geostationary Operational Environmental Satellite AVHRR – Advanced Very High Resolution Radiometer HRV – High Resolution Visible HRVIR – High Resolution Visible and Infrared HRG – High Resolution Geometric ...

Vineesh V, Geography

Search This Blog