Different types

"In passive imagery systems, sensors are designed to detect electromagnetic emissions from constituents of the Earth's surface and atmosphere. These emissions can be locally produced (e.g. thermal radiation from vegetation in the infrared spectrum) or be the result of reflected sunlight in the visible spectrum."https://business.esa.int/newcomers-earth-observation-guide#ref_2.2.1

Example: Hyper-spectral

"Erspectral imagery aims at obtaining a nearly-continuous spectrum for each pixel in the image of a scene, extending the benefits of multi-spectral imagery, which measures light intensity on a limited number of separate bands of the electromagnetic spectrum. " https://business.esa.int/newcomers-earth-observation-guide#ref_2.2.1

"In active imagery systems, instruments are composed of a transmitter that sends out a specific electromagnetic signal and of a sensor receiving the interaction of the signal with the Earth’s surface. Such observations are not dependent on solar illumination."https://business.esa.int/newcomers-earth-observation-guide#ref_2.2.1

Example: Radar Scatterometry

"The radar scatterometer measures the backscatter from small (cm) waves at the sea surface, at skew incidence angles. From these sea roughness measurements the wind vector at 10 m height is calculated. Radar scatterometer data are important sources of information for Numerical Weather Prediction (NWP), oceanography and climate studies. "https://business.esa.int/newcomers-earth-observation-guide#ref_2.2.1

"Atmospheric Chemistry can be monitored using a range of EO instruments using various techniques and different parts of the electromagnetic spectrum. Each atmospheric gas is characterised by its “absorption” and “emission” spectra, which describe how the molecules respond to different frequencies of radiation. EO remote sensing instruments exploit these “signatures” to provide information on atmospheric composition, using measurements over a range of wavelengths between UV and microwave. " https://business.esa.int/newcomers-earth-observation-guide#ref_2.2.1