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

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...

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 ...

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...

Lidar

LiDAR (Light Detection and Ranging) is an active remote sensing technology that measures distances by illuminating a target with laser pulses and analyzing the time it takes for the reflected light to return. Unlike passive systems (e.g., cameras, multispectral sensors), LiDAR provides its own energy source (laser), allowing it to operate both day and night and even penetrate through vegetation canopies . 🔹 How LiDAR Works (Step-by-Step Process) Laser Pulse Emission The system emits rapid, short pulses of laser light (commonly in the near-infrared wavelength, 1064 nm ). Some systems emit up to hundreds of thousands of pulses per second . Interaction with Target Surface The laser beam strikes objects such as vegetation, buildings, or bare ground. Depending on the object's structure, part of the pulse may scatter or reflect. Return Signal Detection The sensor records multiple returns : First Return → typically vegetation canopy tops. ...

Vineesh V, Geography

Search This Blog