Month: June 2020

Understanding Errors and Distortion in Remote Sensing

The old saying “garbage in, garbage out” is true of many situations, and in remote sensing, it’s spot on. The insight you gain from a data set is only as good as the data you source.

Distortion in aerial photography or metadata inconsistencies can botch results, impacting project cost, deadlines, and even safety. When estimating vegetation growth for fire prevention or tracking hillside erosion in residential areas, for example, remote sensing accuracy can become a matter of life and death.

Accurate data from remote sensing technology is fuel for process automation, 3D immersive mapping, advanced security, and much more. But how do you detect errors and distortions that can undermine data integrity?

Understanding resolution

To understand how errors in remote sensing occur, we first need to understand what factors are at play in data generation.

Photogrammetry relies on high-resolution images to quantify measurements and form 3D models of buildings, infrastructure, property, and more. This aerial photography involves a number of different forms of data resolution that expand on our general understanding of picture quality. Resolution in photogrammetric data comes in three distinct forms:

Spatial Resolution

Spatial resolution describes the area and detail of the smallest feature that can be detected by a remote sensing device. It’s usually described by a single value representing the length of one side of a square pixel. In other words, a spatial resolution of 100m means that one pixel represents an area of 1,000 sq/meters on the ground.

The finer the spatial resolution, the more precise the data in each pixel — and the more refined your spatial analysis can be.

Spectral Resolution

Light and color can be incredibly valuable indicators of on-the-ground conditions, or infuriating sources of errors and distortions. It all depends on how accurately they’re documented.

Spectral resolution describes the capacity of a sensor to document electromagnetic wavelengths (which could include color, infrared light, and more). The finer the spectral resolution, the narrower the range that a sensor can document.

Color and shadow matter for most projects, but this factor is especially important for satellite-mounted technology — extra layers of atmosphere can become sources of geometric distortions in remote sensing.

Temporal resolution

When too much time passes between two data sets, the continuity necessary to draw solid conclusions is lost. This loss of continuity is the effect of poor temporal resolution.

Similarly, older data sets may no longer meet requirements for accuracy and precision in spatial or spectral resolution, creating inconsistencies and clouding results.

Thankfully, new UAV-mounted remote sensing devices make collecting data and improving temporal resolution on data sets affordable.

Avoiding errors in remote sensing

To reduce distortion and other accuracy issues, consider the following factors:

Atmospheric conditions

Changes in the atmosphere, sun illumination, and viewing geometries during image capture can impact data accuracy, and result in distortions that can hinder automated information extraction and change detection processes. Humidity, water vapor, and light are common culprits for errors and distortion.

When atmospheric conditions change, reference points can be obscured or lost, which impacts efforts to create accurate measurements from images. Differences in light temperature can lead to color changes that distort data quality, and make for unsightly inconsistencies that ruin the magic of 3D maps.

Altitude and reflectance

Light collected at high elevation goes through a larger column of air before it reaches the sensor. The result is surface reflectance, a phenomena which can diminish color quality and detail in images.

The difference in reflectance near the surface and at top-of-atmosphere creates substantial changes in color, image resolution, and perspective that may need to be accounted for in normalization. Even on a small scale, variances in altitude between data sets should raise a red flag for cross-referencing and review.

Documented metadata for cross-referencing

Many data errors come from sources that are difficult to pinpoint — momentary glitches in connectivity, inconsistencies in light or other atmospheric distortions in remote sensing. And unfortunately, the sources of errors in GIS aren’t always immediately apparent.

Metadata is data that describes data—in this case, characteristics of the collected GIS data. In photogrammetry, metadata could include notes related to GPS location, focal length and resolution settings, altitude, time/date, atmospheric conditions, and more. Metadata should tell you who made the data, provide context for the data, and help determine if the data is appropriate for your project.

For researchers and engineers, metadata offers valuable insight into the conditions in which a data set was created and, in many cases, the overall value it creates for a project. Using data sets with incomplete or inconsistent metadata will likely cause erroneous results and should be avoided.

False accuracy is a problem. Good data practices involve regularly layering and cross-referencing data sets against existing data to pinpoint errors and ensure accuracy. Always check your metadata when cross-referencing.

Control over the flight path

Photogrammetry relies on the stability of several factors to produce accurate and precise results. Unfortunately, some of the biggest tools used in remote sensing are among the least reliable.

Airplanes and helicopters are traditionally used in aerial photography. However, both are susceptible to changes in weather and wind speed, not to mention human error — which makes them unreliable for generating bulletproof data sets for advanced mapping software.

Thankfully, UAV technology offers increased control over flight paths. Drones can also fill the temporal resolution gap by flying frequent tours for less than a single manned flight.

Conclusion

Leveraging a data processing solution that allows for up-to-date, reliable data is vital for project success.

Aerial’s new Mapware photogrammetry software generates bigger, better 3D maps in the cloud, so you can access them from anywhere. Whether you want to map a single building, a dozen cell towers, or an entire city, this software comes backed by a team with the expertise needed to create value for your project.

Lidar vs Photogrammetry: Types of Remote Sensing

As remote sensing technology continues to develop and improve, we’re seeing more uses and opportunities to create value in new industries and fields of study — from environmental science to public safety to telecommunications.

Several different remote sensing methods are available today, and each comes with strengths and limitations. Some will be well suited for one application, but not others. How do you determine which is best for your industry?

In this post, we’ll go over two popular remote sensing technologies — LiDAR and photogrammetry — and discuss some key differences between them.

How does LiDAR work?

LiDAR uses basic physics and geometry to uncover remarkable insights. To do so, it uses the power of a laser directed down toward the earth surface and fired in rapid succession — in most cases, a rate of many thousand pulses per second.

The amount of time it takes for the light to return to the LiDAR source indicates its exact distance. It works like echolocation in bats or submarines, but powered by the incredible speed of light (about 186,000 miles per second, if you’re keeping score at home).

Data generated by LiDAR sensors is collected and pinned to GPS metadata to create a detailed map of the landscape. To produce an accurate picture, data from remote sensing tech is then layered to cross-reference ground points and flag errors and inaccuracies.

A LiDAR instrument typically uses three component pieces to collect data. First, a laser produces light that is used as the measurement medium. Reflected light from the ground is collected by the photodetector sensor and optics, and a GPS receiver documents the exact position of thousands of data points in real time.

4 popular remote sensing use cases for LiDAR

  • Surveying
  • Augmented reality
  • Automated driving
  • Hazard assessment on lava flows, landslides, tsunamis, and floods

How does photogrammetry work?

The defining feature of photogrammetry is the use of ultra high resolution aerial photography. 

By capturing multiple images over a landscape, a “stereo” version is produced that provides software with differing views of a single focal point (for an example of how this works, look at a nearby object and rotate closing one eye and then the other). This shifting perspective creates scale that is used to create a composite image with accurate, measurable definition.

These photographs can collect enormous amounts of data from huge swaths of land. Like LiDAR, photogrammetry can be used to survey structures or property with incredible accuracy. In addition, this remote surveying method produces a photographic document of on-the-ground conditions that can be used to perform surveillance, track changes in an environment, or to create 3D interactive maps of a property.

5 popular remote sensing use cases for photogrammetry

  • Construction
  • Mining
  • Telecommunications
  • Oil & gas
  • First response

LiDAR vs Photogrammetry: A 2 Minute Primer

Remote sensing allows people to capture and collect important environmental or structural data faster and more accurately than ever before. Here’s a breakdown on two popular data collection practices:

What is LiDAR?

LiDAR, or light detection ranging, uses points of light to create a detailed map of an object’s position in space. It has been used to power everything from automated driving technology to augmented reality to advanced topographic surveying.

When mounted from a UAV or airplane, LiDAR can be used to directly measure the height and density of land and vegetation below, including detailed data on groundcover and trees. This remote sensing method is valuable for mapping structure, density, and other local characteristics of large land parcels from overhead.

What is photogrammetry?

Photogrammetry uses image overlap and UAV-captured images to produce a robust 3D composite of a region. 

By using ultra high resolution image collection, in concert with advanced GPS and mapping software, photogrammetry can produce a fully immersive 3D visual model of the real world. 

More than a survey map, this process creates an interactive photographic artifact that can be deployed by environmental agencies, industry, and more.

Popular Use Cases for LiDAR and Photogrammetry

LiDARPhotogrammetry
Mining and geology
Forestry management
Hazard assessment
Agriculture
Construction
Telecommunications
Oil & Gas
First response
Surveying

What else can remote sensing do? Here are some examples in the news from across various industries and disciplines:


Want to learn more about remote sensing technology? Read our Complete Guide to Remote Sensing.

What sets LiDAR and photogrammetry apart?

Both LiDAR and photogrammetry are highly accurate for surveying buildings, infrastructure, and raw land. LiDAR can collect more detailed depth information than photogrammetry, but photogrammetry includes detailed visual information on the environment that is indispensable for many researchers.

When it comes to dollars-and-cents decision making, LiDAR tends to be more costly and more difficult to set up and calibrate — especially when mounted on surveying airplanes and helicopters. Thankfully, the cost of both photogrammetry and LiDAR are dropping thanks to widespread adoption of UAV technology across industries.

Read about how UAV photogrammetry can go beyond surveying and mapping to cut costs, improve data quality, and transform entire industries.

Choosing the right data processing solution

Selecting the right approach to mapping is the first step, but finding the right partner for the job is equally important. Mapware has the remote sensing technology and the expertise to create value for you and your customers.

Mapware’s photogrammetry software is the best tool for the job, whether you want to map a single building, a dozen oil derricks, a protected wetland, or an entire city. This software suite generates bigger, better 3D maps that are fully cloud accessible for use in the field.