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Active vs Passive Sensors

A woman holding a smartphone showcasing network communications.

You’d be surprised to find that you can find out information about an object without having to make any physical contact with it. Having the advantage of collecting large amounts of data using technological instruments is a significant step towards a cutting-edge future.

If you want to find out more about how you can obtain data from objects remotely, keep on reading. 

What is Remote Sensing Technology?

Let’s say you want to detect and monitor the physical characteristics of your area. To go about this, you’d need to know how to measure the emitted and reflected radiation from a distance. The most typical distance that’s ideal is from a satellite or an aircraft.

This is what’s called using remote sensing technology. While remote sensing is the process that you’d use to determine your results.

You need to have specialized cameras to ensure that you remotely collect these sensed images. You’d be surprised to find that researchers can use these images to learn more about the Earth. 

If you want to find out the typical uses of your sensed images, read these examples below. 

  • You can map large forest fires with your images that are collected from space. This can help rangers to see more from below. 
  • Your sensed images can assist meteorologists to predict the weather. This should help to track any potentially dangerous weather conditions. 
  • You can assist town planners to track the growth of new cities. These changes can span several decades. 
  • Your images can help to discover and map the rugged topography of deep canyons, mountain ranges, and other interesting parts of the ocean floor. 
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Types of Remote Sensors 

Remote sensing isn’t as simple as you might think. For instance, you should have an idea of the types of remote sensors that you need to use. In addition, you should understand their differences to better understand what might work best for your innovative ideas.

According to the National Aeronautics Space Administration (NASA), these two types of remote sensing instruments can be differentiated as follows. 

Active Sensors 

A top view image that showcases the self-driving sensor technology of the car.

Active sensors are what you call sensors that operate by throwing their energy source towards the Earth. Think of them as sensors that act in a microwave part of the electromagnetic spectrum. Essentially, this is what makes it easier for them to penetrate the atmosphere despite most conditions.

You can use an active technique to view your target from both ends of the baseline. You should know your length though because the distance between your instrument and target can be affected by it. This phenomenon is known as changing the parallax of your instrument and target.

Your active sensors should use the following instruments to achieve your goal.

1. Laser Altimeter 

This is an instrument that can measure the height of your aircraft or spacecraft while it’s above the surface. It uses lidar to determine the topography of your underlying surface area. 

2. Lidar

This is a light amplification that you can use to transfer a light pulse. This pulse is transmitted through a receiver that has sensitive detectors. Let’s say you want to measure your reflected light, this instrument can measure the distance of your object by calculating the speed of light. 

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3. Radar

This sensor not only emits microwave radiation but can also provide its source of electromagnetic power. It measures the detected microwave radiation. The time that it takes for energy to travel back and forth between the target, should determine the distance from your target. 

4. Ranging Instrument

This is simply your device that can measure the distance between your instrument and your targeted object. Your ranging instrument uses active techniques to view your target from either end of its baseline. It can affect the change of the parallax. 

5. Scatterometer 

If you need to measure any backscattered radiation over the ocean floor, then this high-frequency, microwave radar should benefit you.

6. Sounder

If your aim is to measure detailed weather conditions, this instrument allows you to measure the vertical distribution of atmospheric characteristics such as your cloud composition, humidity, and precipitation. 

Passive Sensors 

This is a gadget attached to the house exterior that has radar and passive sensor.

On the other hand, you can use passive sensors to measure reflected sunlight. These sensors are ideal if you want to detect any natural energy that’s reflected by the object that you want to observe. Generally, passive systems can operate in various operations.

For instance, they can operate in both infrared and microwave portion of the electromagnetic spectrum. As a result, they use a combination of radiometers and spectrometers to achieve this goal. They can be summarized as follows. 

1. Accelerometer 

If you want to measure the change in velocity of your per unit time, you have the option of two types of accelerometers. One can measure the changes that occur in your linear motions of more than one dimension. While the other measures the changes that occur during the rotation rate of your per unit time. 

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2. Hyperspectral radiometer

This is a highly advanced sensor that you can use to detect up to hundreds of very narrow spectral bands that travel through the mid-infrared, near-infrared, and visible portions of the electromagnetic spectrum. The result is an extremely high spectral resonance that you can use to facilitate the fine discrimination that you can find between different targets. 

3. Imaging radiometer

Think of a radiometer that can scan your sensed images to provide you with a two-dimensional array of its pixels. You can use a range of detectors to scan your images mechanically or automatically. 

4. Radiometer

This is an instrument that you can use to quantify the intensity of the electromagnetic radiation that you can find on some bands within the spectrum. It can be identified according to the portion that it covers. For instance, you get an infrared, microwave, or visible radiation. 

5. Sounder

As discussed above under the instruments that you typically find in your active sensors, a sounder uses multispectral information to measure vertical distributions of atmospheric activity. 

6. Spectrometer

You can use this instrument to analyze, detect, or measure any spectral content that occurs during electromagnetic radiation. 

7. Spectroradiometer

This is an ideal option to measure the intensity of radiation in multispectral bands. These bands are designed to typically sense any useful information about the physical properties of the Earth’s surface. 

Frequently Asked Questions About Active and Passive Sensors 

What are the differences between active and passive sensors?

Active sensors provide an energy source to illuminate an object. On the other hand, passive sensors measure the energy that’s already available from the object. For example, the speed of light from the Sun. 

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What are benefits of remote sensing?

The most obvious benefit of remote sensing is that it allows you to collect information over vast spatial areas. Secondly, it helps you to characterize various features and objects on the ground. In addition, you have the advantage of monitoring their changes over time using systematic data to analyze your findings. 

What are the disadvantages of using remote sensing?

If you want to achieve accurate measurements, you should calibrate your instruments adequately before you use them. This leaves room for human error. Moreover, the high-resolution data can be hard to store if you don’t have the tools to make it scalable without losing the quality.