The main distinctions are made on: - the nature (passive or active) of the sensing instrument providing the image - the wavelength of the electromagnetic spectrum in which the observation is made. The electromagnetic transparency of the atmosphere, as illustrated below, allows for the observation of Earth’s surface in: - the visible spectrum (0.39 to 0.70 μm) - in a part of the infrared spectrum (from 0.70 to 14 μm) - in the radio wave range (from 1 cm to 11m) ![[Pasted image 20231202154550.png]] 1. [[Passive EO Imagery]] 2. [[Active EO Imagery]] ### Types of EO Data - **Optical** – Images of the Earth using the visible light spectrum (like a georeferenced photograph), some extending into the ultraviolet and infra-red spectrum. - **Radar** – Covering several instrument types, but most notably Synthetic Aperture Radar (SAR) which provides images containing very accurate information about the distance of objects from the sensor - **Video** – short videos captured from space - **Thermal** – Infra-red data which can provide some heat information from space - **Greenhouse gas detection** – Measuring concentrations of gases, such as carbon dioxide, methane, sulphur dioxide, nitrous oxides, etc. - **Meteorology** – commercial weather data - **Positioning, Navigation and Timing (PNT)** – Though not imaging sensors, these provide geospatial information based on Global Navigation Satellite Systems (GNSS) and often with additional data attached, such as Automatic Identification System (AIS) information about ships or Automatic Dependent Surveillance-Broadcast (ADS-B) information about aircraft which can be used together with imagery.