Let's start asking Remote Sensing related questions and get simple focused answers.

1. What is remote sensing?

Starting with a strict definition "remote sensing is the acquisition of information about an object or phenomenon without making physical contact with the object"

This definition is very broach and as a consequence includes vastly different domains like optical imaging, radar imaging, altimetry, magnetometry etc

2. Is earth observation different from remote sensing?

Yes it is different, but still similar. Remote sensing as defined above is the science of measuring and estimating parameters of an object/phenomenon from a distance. So this object/phenomenon can be actually anything. On the other hand, earth observation refers only to part of remote sensing that observes the earth. So we could say that earth observation is included in the broader domain of remote sensing.

3. What is remote sensing technology?

This one is very simple. It refers to the technological sensors used to acquire remote sensing data. And as you see in the next question we actually have different types of remote sensing based on these technologies. 

4. What are the types of remote sensing?

Based on the technology used to capture remote sensing data, we define different types of remote sensing. We have two broad categories passive and active. It refers to whether the signal measured is emitted from the sensor (active) or not (passive) 

4.1 passive remote sensing

4.1.1 multispectral, hyperspectral

Multispectral and hyperspectral remote sensing refers to the measurement of the reflected spectrum ranging from UV wavelengths to shortwave infrared (i.e. 200nm - 25000nm)

4.1.2 thermal

Thermal remote sensing refers to the measurement of the emitted thermal infrared radiation in the 11 - 15 μm spectrum

4.2 active remote sensing

4.2.1 SAR

SAR or Synthetic Aperture RADAR refers to the measurement (in the form of imagery) of the backscatter of the microwave pulse emitted from the sensor.

4.2.2 LiDAR and altimetry

LIDAR, which stands for Light Detection and Ranging, is a remote sensing method that uses light in the form of a pulsed laser to measure ranges (variable distances) to the object sensed. Altimetry is a very similar to the concept of LiDAR, i.e. it measures distances, but it does this with a vertical radar sensor instead of a pulsed laser.

5. What is remote sensing data?

The measurements and information acquired by the sensors. To give a few examples. A multispectral image captured by the multispectral camera is remote sensing data. The information (or metadata) that accompany this image is part of the remote sensing dataset, but as standalone it cannot be considered as such. Also the spectral measurements from a spectrometer (consider it as a one pixel hyperspectral/multispectral image) is also remote sensing data

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About the writer

Dimitris Sykas is a Remote Sensing and Surveying Engineer with a Ph.D. in hyperspectral remote sensing from the National Technical University of Athens (2016). He has spent fifteen years turning satellite data into operational products: at the NTUA Remote Sensing Laboratory, at Planetek Hellas as Senior EO Engineer, at Neuropublic building machine-learning models for smart farming and CAP monitoring, as a postdoctoral researcher on deep learning for agricultural Earth observation at the National Observatory of Athens, and as CTO of the cloudeo group. In 2024 he co-founded GOVADI, an Athens-based company building sovereign, on-premises AI systems for the Greek public sector and large enterprises, where he leads the technical direction of its products: Greek speech-to-text, retrieval-augmented generation with local models and embedding stores, document OCR and PII anonymisation. He has taken part in more than 25 funded EU and ESA projects, has authored over 23 peer-reviewed publications in remote sensing, and holds an international patent in hyperspectral data compression. He founded GEO University to bring hands-on GIS and Earth observation training online.

Dimitris Sykas

Remote Sensing Engineer, Ph.D. · Co-founder and Director, GOVADI · Founder, GEO University