Millimeter Wave Radiometers

Millimeter Wave Radiometers

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The concept of blackbody radiation was introduced in Chapter 3. It was shown that the total power emitted by an object is a function of the temperature, and the emissivity of the material is proportional to T4 as described by the Stefan-Boltzmann law. It was also shown that if the power is measured in a region far from the emission peak, the source brightness, Bf (W/m2/Hz/ sr), is directly proportional to the temperature, T (K), according to the relationship described by the Rayleigh-Jean law (Currie and Brown 1987): Bf = 2kT/λ2 , (4.1) where k is Boltzmann's constant (1.3804 x 10-23 J/K), T is the source temperature (K), and l is the wavelength (m). This approximation is accurate to within 1% for frequencies below 100 GHz, and to within 3% for frequencies below 300 GHz. It can therefore be applied to both microwave and millimeter wave systems (Ulaby 1987).

Chapter Contents:

  • 4.1 Antenna Power Temperature Correspondence
  • 4.1.1 Example of Power Received from a Blackbody
  • 4.2 Brightness Temperature
  • 4.3 Apparent Temperature
  • 4.4 Atmospheric Effects
  • 4.4.1 Attenuation
  • 4.4.2 Downwelling Radiation
  • 4.4.3 Upwelling Radiation
  • 4.5 Terrain Brightness
  • 4.6 Worked Example: Space-based Radiometer
  • 4.6.1 Temperature Contrast
  • 4.7 Antenna Considerations
  • 4.7.1 Beamwidth
  • 4.7.2 Efficiency
  • 4.7.3 Fill Ratio
  • 4.8 Receiver Considerations
  • 4.8.1 Mixer Implementations for Microwave Receivers
  • Mixer Specifications
  • 4.8.2 Noise Figure
  • 4.9 The System Noise Temperature
  • 4.10 Radiometer Temperature Sensitivity
  • 4.11 Radiometer Implementation
  • 4.11.1 Total Power Radiometer
  • 4.11.2 Dicke Radiometer
  • 4.11.3 Performance Comparison between Radiometer Types
  • 4.12 Intermediate Frequency and Video Gain Requirements
  • 4.13 Worked Example: Anti Tank Submunition Sensor Design
  • 4.13.1 Radiometer Implementation
  • 4.13.2 Receiver Noise Temperature
  • 4.13.3 Minimum Detectable Temperature Difference
  • 4.14 Radiometric Imaging
  • 4.14.1 Image Processing
  • 4.15 Applications
  • 4.15.1 Airborne Scanned Millimeter Wave Radiometer
  • 4.15.2 Scanning Multi-channel Microwave Radiometer (SMMR)
  • 4.15.3 Ground Based Millimeter Wave Radiometers
  • Low Visibility Imaging
  • Concealed Weapon Detection
  • Surveillance and Law Enforcement
  • Medical Imaging
  • 4.15.4 Radio Astronomy
  • Single Dish Telescopes
  • Telescope Arrays
  • Applications
  • 4.16 References

Inspec keywords: radiometers; constants

Other keywords: microwave wave systems; blackbody radiation; Stefan-Boltzmann law; source brightness; emission peak; material emissivity; millimeter wave systems; millimeter wave radiometers; Boltzmann constant; Rayleigh-Jean law

Subjects: Sensing devices and transducers

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