Land Cover Change Monitoring change over time Ned Horning Director of Applied Biodiversity Informatics

Land Cover Change change image early date late date

Why monitor land cover change? Identify areas of deforestation/reforestation Identify areas of deforestation/reforestation Monitor growth of urban or rural populations Monitor growth of urban or rural populations Predict future change based on past change Predict future change based on past change Provide data for climate or carbon budget models Provide data for climate or carbon budget models Monitor changes in species habitat Monitor changes in species habitat Monitor changes in agriculture patterns Monitor changes in agriculture patterns

What are the options for output products? Classified maps Classified maps Statistics Statistics Image maps Image maps

Classified maps The most familiar type of land cover change product The most familiar type of land cover change product Provides “wall- to-wall” mapped output Provides “wall- to-wall” mapped output Typically costly and time consuming Typically costly and time consuming

Statistics Common during the early years of remote sensing Common during the early years of remote sensing Relies on sampling statistics Relies on sampling statistics Primary disadvantage is that accuracy is lower and mapped output is not created Primary disadvantage is that accuracy is lower and mapped output is not created Forest unchanged 6271 Hectares 67.4% Non-forest unchanged 2823 Hectares 30.3% Deforestation 212 Hectares 2.3% Total area 9306 Hectares 100%

Visual change image Very quick and easy method for illustrating change Very quick and easy method for illustrating change Requires minimal skill to create the visualization Requires minimal skill to create the visualization Red = Band 5 most recent image Red = Band 5 most recent image Green = Band 5 older image Green = Band 5 older image Blue = Band 5 older image Blue = Band 5 older image Interpretation requires familiarity of the landscape Interpretation requires familiarity of the landscape No quantitative/classified product is produced No quantitative/classified product is produced

Classification approaches Post classification Post classification Multi-date composites Multi-date composites Image math Image math Spectral change vectors Spectral change vectors On-screen digitizing/editing On-screen digitizing/editing On-screen swipe or flicker On-screen swipe or flicker Multi-temporal RGB image Multi-temporal RGB image Hybrid approaches Hybrid approaches

Comparing two classified images (post-classification) Very intuitive Very intuitive Rarely the most accurate because errors from each land cover classification are added together Rarely the most accurate because errors from each land cover classification are added together Early dateLate dateChange image

Multi-date composite classification Combines imagery from two dates into a single multi-date image Combines imagery from two dates into a single multi-date image Multi-date image is classified using the automated classification method of choice Multi-date image is classified using the automated classification method of choice Advantage is that change classes are directly output Advantage is that change classes are directly output Often the method of choice Often the method of choice

Image math Uses single-band products (i.e., image bands or NDVI) from each date Uses single-band products (i.e., image bands or NDVI) from each date Easy and fast to compute Easy and fast to compute Output shows areas that have changed from one date to the next Output shows areas that have changed from one date to the next Often used to create a mask highlighting areas that have undergone some sort of land cover change Often used to create a mask highlighting areas that have undergone some sort of land cover change TM band 5 early dateTM band 5 late date Difference image Image mask white = change

Spectral change vectors Produces a magnitude of change image (similar to image math) and a direction of change image Produces a magnitude of change image (similar to image math) and a direction of change image

On-screen swipe or flicker Visual assessment only Visual assessment only Often used to help with on-screen digitizing Often used to help with on-screen digitizing

Multi-temporal RGB image Visual assessment only Visual assessment only Often used to help with on-screen digitizing Often used to help with on-screen digitizing Red=band 5 late date Red=band 5 late date Green=band 5 early date Green=band 5 early date Red=band 5 early date Red=band 5 early date

On-screen digitizing / editing Sometimes called heads-up digitizing Sometimes called heads-up digitizing Visual methods are used to manually outline areas that have been visually identified as changing from one cover type to another Visual methods are used to manually outline areas that have been visually identified as changing from one cover type to another Editing/updating previous land cover maps with more recent imagery can provide a reliable land cover change map Editing/updating previous land cover maps with more recent imagery can provide a reliable land cover change map Requires familiarity of landscape Requires familiarity of landscape

Hybrid approach Uses a combination of manual and automated classification methods Uses a combination of manual and automated classification methods Use automated methods to classify the image and then manual methods to edit the classification Use automated methods to classify the image and then manual methods to edit the classification Use automated methods to classify the “easy” classes and manual methods for the rest Use automated methods to classify the “easy” classes and manual methods for the rest Use automated methods to create land cover for one date then edit the land cover map to determine change Use automated methods to create land cover for one date then edit the land cover map to determine change

Dealing with different data sources Difficult/impossible to use similar imagery when conducting land cover change over a long time period Difficult/impossible to use similar imagery when conducting land cover change over a long time period On-screen digitizing works well since the human brain is pretty good and sorting through the different image qualities when using multiple image types On-screen digitizing works well since the human brain is pretty good and sorting through the different image qualities when using multiple image types Post-classification is an alternative if automated methods are preferred Post-classification is an alternative if automated methods are preferred

What about data normalization Goal is to make the two images similar with respect to radiometric and geometric qualities Goal is to make the two images similar with respect to radiometric and geometric qualities Accurate image-to-image registration is very important when using automated methods to avoid false change due to offset pixels between dates Accurate image-to-image registration is very important when using automated methods to avoid false change due to offset pixels between dates Image-to-image registration is more important than absolution image registration Image-to-image registration is more important than absolution image registration Radiometric normalization reduces the change in pixel value between two dates caused by factors other than changes in land cover Radiometric normalization reduces the change in pixel value between two dates caused by factors other than changes in land cover

Issues to consider Sensor characteristics (resolution, radiometric) Sensor characteristics (resolution, radiometric) Solar illumination / seasonality Solar illumination / seasonality Soil moisture Soil moisture Acquisition date and frequency Acquisition date and frequency Water levels (tide, river and lake level) Water levels (tide, river and lake level)

Vietnam case study Change detection in central Vietnam Change detection in central Vietnam Wanted to monitor changes in land cover from the early 1960’s to the present Wanted to monitor changes in land cover from the early 1960’s to the present Wanted to use four or five time periods Wanted to use four or five time periods Decided to use ASTER, Landsat ETM+, Landsat TM, Landsat MSS, Corona, and aerial photography. Decided to use ASTER, Landsat ETM+, Landsat TM, Landsat MSS, Corona, and aerial photography. Use visual methods primarily Use visual methods primarily

Historical land cover change in Central Vietnam Red-shanked Douc Langur Saola Understand critical biodiversity needs Determine how the landscape has taken shape Support the development of protected areas Giant Muntjac

Vietnam’s Central Truong Son

Digital color infrared Acquired: April 21, 2003 Spatial resolution: 30 meters Landsat ETM+

Landsat TM Digital color infrared Acquired: February 17, 1989 Spatial resolution: 30 meters

Digital color infrared Acquired: March 14, 1975 Spatial resolution: 57 meters Landsat MSS

Panchromatic (b/w) film Acquired: March 2, 1969 Spatial Resolution: 3 meters Corona