The Ministry of Environment presented the scientific methods and techniques that its working group in charge of forest cover assessment employed in its 2020 survey. The results of the assessment are scheduled to be released this year.
The techniques and methodology were presented in a more than 10-minute video clip titled “Production of forest cover resources of Cambodia” as the final report of the assessment is prepared.
Ministry undersecretary of state Chuop Paris said in the video that it is important as it will provide up-to-date exact figures of how much forest remains in the Kingdom, and will catalogue it by type – that is, how much is dense forest, semi-dense forest, bamboo forest, grassland and how many hectares of waterways there remain in Cambodia.
He said the assessment is conducted every two years in accordance with the Climate Change Report.
“We are a member of the UN and we are also a member of the UN Framework Convention on Climate Change, so we need to make sure the figures are accurate,” he said.
Huot Nabory – director of the Office of Geographical Information Services under the ministry’s General Department of Environmental Knowledge and Information – said the interpretation of forest cover resources is conducted in four major stages: firstly through satellite imagery; secondly, through thorough analysis and interpretation of the imagery, using geographic information systems; thirdly with verification of the level of reliability of the results produced by the team; and finally, statistics are calculated which show Cambodia’s forest cover resources.
She said the team used a variety of satellite imagery, which had cloud coverage of 10 per cent. The team also downloaded images via Google Earth Engine, a geospatial processing service that downloaded the images with less than 10 per cent cloud cover, before processing the images.
“We collated the pictures and then segmented them automatically. The next step was to conduct a Principle Components Analysis, or PCA – using the AGeS programme – to find out where forest cover resources are changing, and where we see declines or increases,” she said.
Nabory added that after the PCA is carried out, the team classifies the satellite imagery in two stages. The first is called automatic classification and has two major categories: forest land and non-forest land classification.
After obtaining the results of this preliminary ranking, the team works out 22 detailed rankings using the experience of the classifier. Each team member uses their eyes to determine the rankings and take note of any variations.
“In order to confirm the accuracy of these 22 rankings, we verify each step and make adjustments to the rankings that we find to be abnormal. We make these corrections first before we estimate the points for field verification,” she said.
Ministry spokesman Neth Pheaktra said on April 20 that the video was released to help explain how the ministry arrived at the results of the upcoming report.
“The results will accurately reflect what the assessment has found. We do not use only one source for images, and the video should make it clear that the ministry has approached this task with a great sense of responsibility,” he said.
According to the results of the 2018 Cambodia Forest Resource Assessment – published by the ministry in September last year – the Kingdom’s forest area was approximately 8,510,807ha, equivalent to 46.86 per cent of the country’s total land area.
Cambodia conducted eight national forest cover assessments between 1973 and 2018.
The ministry set up the nationwide land use mapping and forest cover group in collaboration with national experts from various ministries and institutions and development partners, relevant UN bodies as well as international universities.