11.1 Principles of remote sensing for planetary studies

Remote sensing revolutionizes planetary science by letting us study distant worlds without setting foot on them. From mapping surfaces to probing atmospheres, it's our cosmic Swiss Army knife for unraveling planetary mysteries.

But it's not all smooth sailing. Resolution limits, lack of ground truth, and data overload can make interpreting remote sensing info tricky. Still, it's our best bet for exploring the solar system from afar.

Remote sensing principles for planetary science

Fundamental concepts and techniques

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• Remote sensing acquires information about an object or phenomenon without physical contact by detecting and measuring electromagnetic radiation reflected, absorbed, or emitted by the target
• Passive remote sensing relies on natural energy sources (sunlight) to illuminate the target
• Active remote sensing uses artificial energy sources (radar, lidar) to actively probe the target
• Spectroscopy studies how matter interacts with electromagnetic radiation at different wavelengths
  • Spectral signatures provide information about composition, temperature, and physical properties of the target

Data characteristics and applications

• Spatial resolution refers to the smallest resolvable object by a remote sensing system
  • Higher spatial resolution allows for more detailed observations of surface features and structures
• Temporal resolution refers to how frequently a remote sensing system can acquire data over the same area
  • Higher temporal resolution enables monitoring of dynamic processes and changes over time
• Remote sensing data applications in planetary science
  • Create detailed maps of planetary surfaces
  • Study atmospheric composition and dynamics
  • Investigate surface composition and mineralogy
  • Monitor changes in surface features over time

Remote sensing instruments in planetary exploration

Passive sensors

• Cameras capture visible light to create images of planetary surfaces
  • Examples: HiRISE camera (Mars Reconnaissance Orbiter), Cassini ISS camera system
• Spectrometers measure the intensity of electromagnetic radiation at different wavelengths, providing information about composition and properties of the target
  • Types of spectrometers: visible/near-infrared (VNIR), thermal infrared (TIR), gamma-ray spectrometers
  • Example: CRISM (Compact Reconnaissance Imaging Spectrometer for Mars) on Mars Reconnaissance Orbiter

Active sensors

• Radar (Radio Detection and Ranging) instruments use radio waves to probe planetary surfaces
  • Provides information about surface roughness, topography, and subsurface structure
  • Examples: MARSIS and SHARAD radar systems (Mars Express and Mars Reconnaissance Orbiter)
• Lidar (Light Detection and Ranging) instruments use laser pulses to measure the distance to a target
  • Creates high-resolution topographic maps
  • Example: LOLA instrument (Lunar Reconnaissance Orbiter)
• Magnetometers measure magnetic fields, providing insights into internal structure and evolution of planetary bodies
  • Example: MAG instrument (Juno spacecraft) studying Jupiter's magnetic field
• Gravimeters measure subtle variations in gravitational fields, revealing information about internal mass distribution of a planetary body
  • Example: GRAIL mission used twin spacecraft to map the Moon's gravitational field in high resolution

The electromagnetic spectrum in planetary remote sensing

Regions of the electromagnetic spectrum

• The electromagnetic spectrum encompasses all frequencies and wavelengths of electromagnetic radiation (radio waves to gamma rays)
• Different regions of the electromagnetic spectrum interact with matter in distinct ways, providing unique information about the target
• Visible light (380-700 nm): Detectable by human eyes, cameras operating in this range capture images similar to what we would see
• Infrared radiation (700 nm - 1 mm): Associated with heat emission, thermal infrared remote sensing provides information about surface temperature and thermal properties
• Near-infrared (NIR) and short-wave infrared (SWIR): Sensitive to the presence of water, hydrated minerals, and organic compounds, useful for studying the composition of planetary surfaces

Interactions with planetary surfaces and atmospheres

• Ultraviolet (UV) radiation (10-380 nm): Used to study atmospheric composition and dynamics, as well as surface materials that absorb or reflect UV light differently
• Radio waves (wavelengths > 1 mm): Can penetrate surface materials, allowing for the study of subsurface structure and properties
  • Radar remote sensing utilizes radio waves to create images and maps of planetary surfaces
• Atmospheric interference: For planets with substantial atmospheres (Venus, Titan), atmospheric scattering, absorption, and refraction can limit the ability to observe surface features and properties

Advantages vs limitations of planetary remote sensing

Advantages

• Enables study of planetary bodies without direct contact, allowing observations of inaccessible or hazardous environments
• Global coverage: Orbiting spacecraft can provide comprehensive coverage of an entire planetary body, allowing for the study of large-scale features and processes
• Multi-scale observations: Data can be acquired at various spatial resolutions, from global-scale maps to high-resolution images of specific regions of interest
• Spectral information: Instruments can collect data across a wide range of wavelengths, providing valuable information about composition, physical properties, and processes occurring on planetary surfaces and in their atmospheres
• Temporal monitoring: Repeated observations over time enable the study of dynamic processes, seasonal changes, and long-term evolution of planetary bodies

Limitations

• Resolution limitations: Spatial, spectral, and temporal resolution of remote sensing data is limited by instrument capabilities and distance from the target, restricting the level of detail that can be observed
• Ground truth validation: Interpreting remote sensing data often requires validation through in-situ measurements from landers, rovers, or sample return missions to confirm the accuracy of the observations
• Data volume and processing: Remote sensing missions can generate large volumes of data that require significant computational resources and specialized software for processing, analysis, and storage
• Technological constraints: Instrument design, power requirements, data transmission, and spacecraft limitations can restrict the capabilities of remote sensing missions