Role of Historical Aerial Photographs in Assessing Land-use/Land-cover Changes

By Himanshu Pahava and Divjot Kaur, Published on: 21st December 2020

Human activities and natural phenomena such as population growth, deforestation, industrial expansion, local climatic conditions, and natural disasters cause massive Land-use & Land-cover (LULC) disruptions. In 2018, United Nations published a report on global land-use and land-cover changes showcasing the decline of global forest land by almost 4% since 1990, while urban area doubled.

These land changes majorly impact ecosystems and environmental processes such as climate change, biodiversity, land degradation, deforestation and many more at local, regional and global level.

Therefore, extracting information about LULC changes is a primary requirement for a better understanding of the relationship and interaction between humans and the natural environment, to analyze its impact and minimize its over-lasting effects.

Monitoring and analyzing these LULC changes are of utmost importance for a planned and sustainable development of natural resources and urban growth management.

What are the Sources for Identification of LULC Changes? 

Remote sensing imageries (i.e. images or data collected mostly through satellite, aircraft and drone of land surface) are major data sources for analyzing and extracting Land-use/Land-cover changes.

These multi-temporal (i.e. collected over different time period) remote sensing datasets, prominently, satellite and aerial imagery, help companies to map and identify LULC changes that are impacting the society at large.

However, aerial photographs with their ease of availability provide the best means to assess the long-term changes much earlier than, satellite-based remote sensing images came into existence.

What are the Advantages of Aerial Photography for Assessing LULC Changes?

Aerial photographs provides an accurate visual record of LULC changes. After World War 1, many developed countries across the globe undertook aerial surveys to fulfill the military demand and produce civilian maps over critical territories.

These countries were able to keep most of the archives of these historical aerial photographs safe and in good condition over such a long period. Since last couple of decades, these developed countries have digitized their archives of historical imagery serving as an exclusive source to account high quality LULC information over the past 100 years.

Another important advantage of aerial photography is that accurate height / 3D information can be retrieved by taking measurements from a series of overlapping photographs through a technique called photogrammetry.

Additionally, this extracted height information can be used to generate 3D digital models of real word objects in the form of Digital Terrain Model (DTM) and Digital Surface Model (DSM).

What are the Major Challenges in Obtaining Historical Aerial Imagery?

Most of the historical aerial surveys conducted from early nineteenth century to its last decade were photogrammetric surveys. By utilizing advanced photogrammetric data processing techniques, high quality ortho-rectified mosaic (topographically corrected & matched with geographic coordinate system) and 3D information such as Digital Terrain Model (DTM) & Digital Surface Model (DSM) were produced.

Despite having meaningful qualitative information, there are significant technical constraints in retrieving such information through historical aerial photographs photogrammetric processing, which in itself is a technically complicated and time consuming process. Some of the significant technical constraints observed during the process are listed below:

  • Difficult to overlap adjacent aerial photographs
  • Lack of flight map / data
  • Missing camera calibration information
  • Poor scanning and radiometric quality
  • Difficulties in locating ground control points (GCPs) in changing landscapes

How is RMSI helping to Process Historical Aerial Photo Imagery?

RMSI has utilized its vast experience & expertise in photogrammetry to address this long standing industry challenge of extracting landuse / landcover information from historical aerial photographs. RMSI has developed a customized workflow to overcome the above mentioned technical constraints and deliver high quality output such as ortho-rectified aerial imageries and mosaic, Digital Terrain Model (DTM), Digital Surface Model (DSM), Landuse / Landcover Change Maps.

The customized workflow uses a combination of best available COTS and in-house developed tools. It has semi-automated processes for quality checking, extraction of LULC changes, and LU/LC change assessment. RMSI has also developed an innovative Machine Learning based solution for automated and accurate extraction of LULC changes from a variety of high resolution satellite / aerial imageries.

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