Quantum Theory of Photons

Quantum Theory and Photons

• Light travels in discrete packets known as 'quanta' or 'photons', forming the basis of electromagnetic (EM) radiation.
• Photons are massless particles that embody electromagnetic force and are emitted when matter is thermally excited.
• Energy of a photon is quantified in electron volts, while energy transfer rate is referred to as flux, measured in watts.
• Planck's equation (Q=hν) determines photon energy, where Q is energy in watts, h is Planck's constant (6.626 x 10^-34 J), and ν is the frequency.
• Quantum energy is inversely related to wavelength: Q = hc / λ; shorter wavelengths correspond to higher energy photons.

Electromagnetic Spectrum

• The electromagnetic spectrum encompasses all frequencies of EM radiation, presenting useful wavelength bands.
• Visible light ranges: Blue (0.4 - 0.5 μm), Green (0.5 - 0.6 μm), and Red (0.6 - 0.7 μm).
• Infrared (IR) is classified into Near IR (0.7 - 1.3 μm), Mid IR (1.3 - 3.0 μm), and Thermal IR (3.0 - 14 μm).
• Microwaves range from 1 mm to 1 m; UV light at 0.4 μm is minimally utilized in remote sensing due to atmospheric scattering.

Scattering and Its Effects

• Scattering involves unpredictable diffusion of radiation by atmospheric particles, affecting remote sensing by reducing image contrast and altering spectral signatures.
• Rayleigh scattering occurs with atmospheric molecules; diffuse reflectance describes equal scattering of reflection, crucial for understanding terrain properties.

Spectral Signature Concept

• Spectral reflectance measures the proportion of reflected energy relative to incident energy, expressed as a percentage.
• Reflectance curves graph % reflectance against wavelength, highlighting specific material characteristics.

Passive Remote Sensing

• Passive remote sensing relies on natural or reflected radiation from targets, exemplified by sensors like the Advanced Very High Resolution Radiometer (AVHRR) and SeaWiFS.

Sensor Types Based on Scanning Process

• Whiskbroom scanners use rotating mirrors to achieve point sensing (e.g., Landsat MSS).
• Pushbroom scanners utilize line arrays of sensors, allowing simultaneous data collection (e.g., SPOT).

Sensor Types Based on EMR Range

• Optical Sensors operate in the optical spectrum (0.3 to 14 mm) for applications like meteorology and ocean monitoring.
• Microwave Sensors function in the microwave spectrum, effective under diverse atmospheric conditions, yet less reliable for identifying water bodies.

Characteristics of Satellite Orbits

• Orbital parameters include orbital period, altitude (low, moderate, or high), apogee, perigee, inclination (commonly 99 degrees for remote sensing), nadir, and ground track projections.
• Swath refers to the area sensed during a satellite pass; overlap and sidelap denote common areas in consecutive images.

Satellite Sensor Types

• Linear Self-scanning Sensors (LISS) for multispectral scanning with various generations (LISS-I to LISS-IV).
• Panchromatic (PAN) sensors collect single-band data; Advanced Wide Field Sensors (AWiFS) enable wide swath observations.
• Variants include Ocean Color Monitor (OCM) and Synthetic Aperture Radar (SAR) for active microwave remote sensing.

Orbit Types

• Sun-synchronous orbits maintain consistent solar illumination conditions for imagery acquired at specific times across different seasons.
• Polar-orbiting satellites capture data while the Earth rotates beneath them.
• Geostationary satellites remain stationary over a specific point for continuous regional coverage.

Applications of Remote Sensing

• Remote sensing imagery can depict various environmental features, evidenced by the optical image of Montreal during the ice storm of 1998, where ice/snow/clouds and vegetation colors are identifiable.