Skip to main content

Radar Sensors in Remote Sensing


Radar sensors are active remote sensing instruments that use microwave radiation to detect and measure Earth's surface features.
They transmit their own energy (radio waves) toward the Earth and record the backscattered signal that returns to the sensor.

Since they do not depend on sunlight, radar systems can collect data:

  • day or night

  • through clouds, fog, smoke, and rain

  • in all weather conditions

This makes radar extremely useful for Earth observation.


1. Active Sensor

A radar sensor produces and transmits its own microwaves.
This is different from optical and thermal sensors, which depend on sunlight or emitted heat.

2. Microwave Region

Radar operates in the microwave region of the electromagnetic spectrum, typically from 1 mm to 1 m wavelength.

Common radar frequency bands:

  • P-band (70 cm)

  • L-band (23 cm)

  • S-band (9 cm)

  • C-band (5.6 cm)

  • X-band (3 cm)

Each band penetrates and interacts with surfaces differently:

  • Longer wavelengths → penetrate vegetation and soil

  • Shorter wavelengths → sensitive to surface roughness

3. Backscatter (Radar Return Signal)

When radar waves hit a surface:

  • some energy is absorbed

  • some energy is transmitted

  • some energy is scattered back to the sensor → backscatter

Backscatter depends on:

  • surface roughness

  • moisture content

  • geometry / slope

  • structure (vegetation, buildings)

  • wavelength & polarization

4. Polarization

Radar signals can be polarized:

  • H (Horizontal)

  • V (Vertical)

Combinations:

  • HH (transmit H, receive H)

  • HV (transmit H, receive V)

  • VH

  • VV

Different polarizations help identify:

  • water

  • vegetation structure

  • urban features

5. Incidence Angle

The angle at which radar wave hits the surface.
It affects backscatter values:

  • Small angle → stronger return from smooth surfaces

  • Large angle → stronger return from rough surfaces

6. Speckle

Radar images contain a grainy noise called speckle, caused by coherent scattering.
Speckle reduction filters (Lee, Frost) are used.

7. SAR (Synthetic Aperture Radar)

SAR is the most widely used radar system.
It creates high-resolution images by combining multiple radar pulses as the satellite moves.

SAR enables:

  • high spatial resolution

  • mapping of large areas

  • detection of small surface changes (millimeters)

How Radar Sensors Work 

1. Transmit microwave pulse

The radar antenna sends pulses toward the Earth.

2. Interaction with the surface

Waves interact with objects:

  • smooth water → low backscatter

  • rough terrain → high backscatter

  • wet soil → strong backscatter

  • vegetation → volume scattering

3. Return signal is received

The sensor measures:

  • strength of backscatter

  • time delay (gives distance)

  • polarization

  • phase information

4. Image is formed

The backscatter intensity is converted into grayscale or colored radar images.

5. Advanced processing (optional)

  • Interferometry (InSAR) for measuring deformation

  • Polarimetric analysis (PolSAR)

  • Change detection

Advantages of Radar Sensors

  • All-weather capability

  • Works day and night

  • Penetrates cloud cover

  • Sensitive to surface roughness and moisture

  • Useful for topographic mapping

  • Can measure surface deformation (mm level)

Applications

🌧 Flood mapping

Radar penetrates clouds → detects water extent during storms.

🛰 Land deformation (InSAR)

Detects earthquakes, landslides, subsidence.

🌲 Forest monitoring

Estimates biomass, canopy structure.

🏙 Urban studies

Detects buildings, road networks, and urban expansion.

🌾 Agriculture

Monitors soil moisture and crop structure.

❄ Snow and ice

Maps glaciers and ice movements.

🌊 Sea and ocean

Monitors waves, oil spills, ships.

Radar Sensors

Spaceborne SAR Sensors

  • Sentinel-1 (C-band)

  • RADARSAT-1/2 (C-band)

  • RISAT-1/2 (C-band)

  • ALOS PALSAR (L-band)

  • TerraSAR-X (X-band)

  • COSMO-SkyMed (X-band)

Airborne Radar

  • AIRSAR

  • UAVSAR


Radar sensors are active remote sensing instruments that transmit microwave radiation and measure the backscattered signal from Earth's surface. They operate in the microwave region, work in all weather conditions, and use concepts like wavelength, polarization, incidence angle, and backscatter to produce images. Radar is widely used for flood mapping, land deformation (InSAR), vegetation studies, soil moisture, and urban analysis.


Comments

Post a Comment

Popular posts from this blog

Accuracy Assessment

Accuracy assessment is the process of checking how correct your classified satellite image is . 👉 After supervised classification, the satellite image is divided into classes like: Water Forest Agriculture Built-up land Barren land But classification is done using computer algorithms, so some areas may be wrongly classified . 👉 Accuracy assessment helps to answer this question: ✔ "How much of my classified map is correct compared to real ground conditions?"  Goal The main goal is to: Measure reliability of classified maps Identify classification errors Improve classification results Provide scientific validity to research 👉 Without accuracy assessment, a classified map is not considered scientifically reliable . Reference Data (Ground Truth Data) Reference data is real-world information used to check classification accuracy. It can be collected from: ✔ Field survey using GPS ✔ High-resolution satellite images (Google Earth etc.) ✔ Existing maps or survey reports 🧭 Exampl...
Post a Comment
Read more

Landsat 8 Band designation and Band Combination.

Landsat 8 Band designation and Band Combination.  Landsat 8-9 Operational Land Imager (OLI) and Thermal Infrared Sensor (TIRS) Bands Wavelength (micrometers) Resolution (meters) Band 1 - Coastal aerosol 0.43-0.45 30 Band 2 - Blue 0.45-0.51 30 Band 3 - Green 0.53-0.59 30 Band 4 - Red 0.64-0.67 30 Band 5 - Near Infrared (NIR) 0.85-0.88 30 Band 6 - SWIR 1 1.57-1.65 30 Band 7 - SWIR 2 2.11-2.29 30 Band 8 - Panchromatic 0.50-0.68 15 Band 9 - Cirrus 1.36-1.38 30 Band 10 - Thermal Infrared (TIRS) 1 10.6-11.19 100 Band 11 - Thermal Infrared (TIRS) 2 11.50-12.51 100 Vineesh V Assistant Professor of Geography, Directorate of Education, Government of Kerala. https://www.facebook.com/Applied.Geography http://geogisgeo.blogspot.com
1 comment
Read more

Change Detection

Change detection is the process of finding differences on the Earth's surface over time by comparing satellite images of the same area taken on different dates . After supervised classification , two classified maps (e.g., Year-1 and Year-2) are compared to identify land use / land cover changes .  Goal To detect where , what , and how much change has occurred To monitor urban growth, deforestation, floods, agriculture, etc.  Basic Concept Forest → Forest = No change Forest → Urban = Change detected Key Terminologies Multi-temporal images : Images of the same area at different times Post-classification comparison : Comparing two classified maps Change matrix : Table showing class-to-class change Change / No-change : Whether land cover remains same or different Main Methods Post-classification comparison – Most common and easy Image differencing – Subtract pixel values Image ratioing – Divide pixel values Deep learning methods – Advanced AI-based detection Examples Agricult...
Post a Comment
Read more

Landsat band composition

Short-Wave Infrared (7, 6 4) The short-wave infrared band combination uses SWIR-2 (7), SWIR-1 (6), and red (4). This composite displays vegetation in shades of green. While darker shades of green indicate denser vegetation, sparse vegetation has lighter shades. Urban areas are blue and soils have various shades of brown. Agriculture (6, 5, 2) This band combination uses SWIR-1 (6), near-infrared (5), and blue (2). It's commonly used for crop monitoring because of the use of short-wave and near-infrared. Healthy vegetation appears dark green. But bare earth has a magenta hue. Geology (7, 6, 2) The geology band combination uses SWIR-2 (7), SWIR-1 (6), and blue (2). This band combination is particularly useful for identifying geological formations, lithology features, and faults. Bathymetric (4, 3, 1) The bathymetric band combination (4,3,1) uses the red (4), green (3), and coastal bands to peak into water. The coastal band is useful in coastal, bathymetric, and aerosol studies because...
Post a Comment
Read more

Development and scope of Environmental Geography and Recent concepts in environmental Geography

Environmental Geography studies the relationship between humans and nature in a spatial (place-based) way. It combines Physical Geography (natural processes) and Human Geography (human activities). A. Early Stage 🔹 Environmental Determinism Concept: Nature controls human life. Meaning: Climate, landforms, and soil decide how people live. Example: People in deserts (like Sahara Desert) live differently from people in fertile river valleys. 🔹 Possibilism Concept: Humans can modify nature. Meaning: Environment gives options, but humans make choices. Example: In dry areas like Rajasthan, people use irrigation to grow crops. 👉 In this stage, geography was mostly descriptive (explaining what exists). B. Evolution Stage (Mid-20th Century) Environmental problems increased due to: Industrialization Urbanization Deforestation Pollution Geographers started studying: Environmental degradation Resource management Human impact on ecosystems The field became analytical and problem-solving...
Post a Comment
Read more