Embed Size (px)
Citation preview
Near-real time monitoring of deforestation using a neural
network and MODIS data: the PARASID approach
Andy Jarvis, Louis Reymondin, Jerry Touval
CIAT and TNC
Contents
• The approach• The implementation• Some examples• Comparison with DETER• Comparison with FORMA• Plans and timelines
Objectives of PARASID
HUman Impact Monitoring And Natural Ecosystems
• Provide near-real time monitoring of habitat change (<3 month turn-around)
• Continental – global coverage (forests AND non-forests)
• Regularity in updates
The Approach
The change in greenness of a given pixel is a function of:
• Climate• Site (vegetation, soil, geology)• Human impact
Machine learning
We therefore try to learn how each pixel (site) responds to climate, and any anomoly corresponds to human impact
Machine learning (or neural-network), is a bio-inspired technology which emulates the basic mechanism of a brain.
It allows – To find a pattern in noisy dataset– To apply these patterns to new dataset
4500
5000
5500
6000
6500
7000
7500
8000
8500
9000
1 2 3 4 5 6 7 8 9Time
NDVI
Measurments
Predictions
Interval max
Interval min
4500
5000
5500
6000
6500
7000
7500
8000
8500
9000
1 2 3 4 5 6 7 8 9Time
NDVI
Measurments
Predictions
Interval max
Interval min
NDVI Evolution and novelty detection
Novelty/Anomoly
What is “machine learning” ?
• Machine learning (or neural-network), is a bio-inspired technology which emulates the basic mechanism of a brain.
• It allows – To find a pattern in noisy dataset– To apply these patterns to new dataset
Methodology
NDVIt
Precipitation (t)
Temperature(t)
…
…
w0
w1
w2
NDVI(t-1)
NDVI(t-2)
NDVI(t-n)
wp1
wp2
wp3
wo1
wo2
wo3
As required by the ARD algorithm, each input and the hidden output is a weights
class with its own α α0
αc
INPUTS: Past NDVI (MODIS 3b42) Previous rainfall (TRMM) Temperature (WorldClim)
OUTPUT: 16 day predicted NDVI
Methodology – Bayesian NN
• To detect novelties, Bayesian Neural Networks provide us two indicators– The predicted value– The probability repartition of where the value should
be
• The first one allows us to detect abnormal measurements
• The second one allows us to say how sure we are a measurement is abnormal.
The Processing
• For South America alone, first calculations approximated 10 years of processing for the NN to learn:– A map of 30720 by 37440 pixels
1,150,156,800 vectors 23 vectors per year 26,453,606,400 NDVI values to manage per year 9.5 years of data 251,309,260,800 individual data points
• Through various processes, optimizations and hardware acquisitions reduced time to 3 months for NN learning
• Detection takes 2-3 days
The Bottom-Line
• 250m resolution• Latin American coverage (currently)• 3 week turnaround from data being made
available (4 week delay in MODIS going to NASA ftp) (3+4 = 7 weeks)
• Report every 16 days• Measurement of scale of habitat change
(0-1) and probability of event
An Example
• Two animations for Mato Grosso
PARASID vs. DETERValidation tests
Validation area
• Location – Brazil– Bottom left corner
• 09°40’00’’ S • 60°00’00’’ O
• Size– 160 * 120 [km2]– 307200 modis pixels
Red square : Validation area
Data source
• Deter dataset has been downloaded on the website of the Deter project : – http://www.obt.inpe.br/deter/indexdeter.php?id=6424
• The satellite images of 2004 and 2006 used to compare the two models are extracted from images – Mosaico LandSat 2004 (AMZ)– Mosaico LandSat 2006 (AMZ)
• Also provide by the Deter project website.
PARASID true positives
2004
2006
Parasid model is, sometimes more sensitive, and detects events that Deter doesn’t detect.
PARASID True Positives
It seems Parasid model detects quite small and isolate events which Deter doesn’t detect.
2006
2004
PARASID False positives
On the other hand, Parasid is more sensitive to false positives. Here, around a river.
2004
2006
PARASID False Positives
In this example, Parasid doesn’t detect as well as Deter the big new field (red circle) but,is more precise to detect the small fields on the top right corner (blue circle) .
2004
2006
Synthesis
• The general locations of detections are the same for both models, so we have in essence created a DETER that works more automatically and is applicable at the continental level
• Both PARASID and Deter models have problems with false positive events, but we can adjust for these using this and other validation data and a genetic algorithm.
• PARASID seems more sensitive for small and isolated events, but this sensitivity may also generate false positives. Again, this is fixable through calibration data.
PARASID vs. FORMAValidation tests
Test area
• Brazil– Latitude 8°36'7.50"S– Longitude 51°28'30.00“W
NDVI 2000.02.18 NDVI 2004.01.01 NDVI 2009.01.01
Models’ output
PARASID detectionsFirst detection in 2004
FORMA probabilitiesFirst detection in 2000
PARASID – FORMA Red pixels show where FORMA’s probabilities are higher than the PARASID onesWhite pixels show where PARASID’s probabilities are higher than the FORMA’s ones
• This map shows the models’ differencies– The two models match
Comparison
Detailed comparison
NDVI 2000.02.18 NDVI 2004.01.01PARASID - FORMA
• The marked areas show that most of the differences are due to the changes which happened between 2000 and 2004.
• Parasid can’t detect these changes as it started detecting in 2004.
Detailed comparison
Top FORMA Bottom PARASIDImages from google earth
PARASID - FORMA
Maybe due to the rescaled pixel size from 250 [m] to 500 [m], FORMA model doesn’t fit perfectly some fields (the red bound around the fields on the comparison map).
Detailed comparison
Top FORMA Bottom PARASIDImages from google earth
PARASID - FORMA
Parasid is a bit more sensitive.
Detailed comparison
Clear change in 2006Softer change in 2008
Maybe vegetation degradation
The pixel plotted is shown in red on the map
.
Detailed comparison
• The two graphs in the previous slide show that the changes detected by PARASID and not by FORMA actually occurred (graph on the right).
• However these changes are more subtle than classic deforestation events (graph on the left).
• This could be due to vegetation degradation (e.g. selective logging) as the area where these changes occurred is surrounded by a high rural activity
• Also some benefits from 250m resolution• PARASID and FORMA complementary in provision of
monitoring
Conclusions and next steps
• Near-real time global monitoring is possible• PARASID now functioning for Latin America• Next milestones:
– Fully functioning web interface January 2010– Continental validation and calibration (January 2010)– Global extent (2011)– Additional models to identify type of change (drivers)
(2011)
