"Complementing Snow Cover Estimation with Analysis of Web Public Images"

DIPARTIMENTO DI ELETTRONICA, INFORMAZIONE E BIOINGEGNERIA

SnowWatch

Complementing Snow Cover Estimation with Analysis of Web Public Images

Roman Fedorov: [email protected]


Introduction

Complementing Snow Cover Estimation with Analysis of Web Public Images 2

• Challenge: transform public images depicting mountain slopes into virtual snow measurement stations.

• Measurements complement existing ground and satellite sensor data


UGC

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Media User Generated Content (UGC) publicly available on the Web is reaching unprecedented size nowadays:• Facebook ~ 350 MM daily photo uploads• Flickr ~ 8.000 MM photographs with 3.5 MM daily

uploads• Panoramio reached ~ 75 MM geo-tagged photograph

It contains an enormous amount of latent implicit knowledge, the challenge is to extract it.



Project

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SnowWatch aims at:• improving snow analysis and water management

through the acquisition and analysis of public media content depicting alpine mountains

• Creating alpine snow media dataset with open contribution of new media and access to processed media and its results for any environmental researchers

The project aims to design, implement and test a new approach to homeland security that combines the traditional measures of the Public Administration with the use of social networks as tools for monitoring and warning the population.



Content Providers

SnowWatch Engine

SnowWatch Architecture

User Photos

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Flickr Photos

Content Consumers

Webcams

API Media Storage

Get Image Orientation, Identify Mountain Peaks

Get Image Snow Pixel-level classification



Flickr Photographs Crawling

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Does an image contain a clear a mountain slope view?

- Heavily depends on thephotograph shooting point altitude



Flickr Crawling Implementation

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SVM Image Content-based Classifier:� Bag of Visual Words / Fisher Vector� SIFT/SSIM/GIST/HOG2x2 Descriptors� Spatial Histogram, Vertical Bands

Manually annotated 1658 samples (~70%) for training and validation and 710 samples (~30%) for testing.



Webcam Images Aggregation

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Identified ~2.000 webcams depicting mountains in Alpine regions.Each webcam produces an image every 1’ – 15’.• 67% of the images are not suitable due to bad weather• More than 50.000 images and 6 GB of data acquired dailyThrough the extraction of the edges we can compute the percentage of the skyline clearly visible, and discard all images with visibility lower than a certain threshold, obtaining the following ROC curve varying the threshold:



Webcam Images Aggregation

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Remaining small moving obstacles (such as low clouds, persons, vehicles) and varying illumination conditions are managed through the median aggregation of all daily images



Photo Peak Identification

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An orientation of a geo-tagged photograph is needed.

Given a Digital Elevation Model (a 3D terrain model) we can simulate the terrain silhouettes that should be seen from the photographer point of view.

Steps� Panorama� Scale� Edges� Filter� Match



Photo Panorama

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Photo Scaling

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Photo must be scaled properly, so the mountains have the same pixel dimension on the photograph and on the panorama.This can be obtained by calculating the Field Of View (FOV) of the photo:




Photo Edge Extraction

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Photo Edge Filtering

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Too many edges on the image that do not belong to a terrain contour!• Skyline detection algorithm is employed, and all the edge

pixels above the skyline are removed, being considered obstacles or clouds.

• Weighting mechanism is applied, which assigns decreasing weights to the edge pixels as the distance from the skyline increases.




Photo Alignment

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Find the best overlap maximizing the vector cross correlation score:




Photo Peak Alignment

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A global overlap between the photo and the panorama is often not enough, a neighborhood vector cross correlation adjustment is applied to each identified peak:

Steps� Panorama� Scale� Edges� Filter� Match� Local Match



Photo Peak Identification

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Fraction of photographs with orientation correctly identified



Snow Pixels Classification

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Classifying each pixel as snow covered/terrain is much more than simply checking bright/dark pixels:




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SnowGround GroundGroundSnow Snow Snow




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Random Forest Classifier that considers pixel and pixel neighbors color, global and local intensity of the image.Trained on 59 manuallylabeled images(~ 7 Million pixels),outperform currentmethods:



Environmental Impact Evaluation

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Environmental consistency evaluation of extracted snow cover indexes.� No direct ground truth, how do we

evaluate it?� Practical utility w.r.t. an environmental

modelUse case: Como Lake water managementFlooding vs Irrigation trend, what is the best solution?



SnowWatch 2°°°° year

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If the physical snow estimations provided by ARPA (Italian EPA) are not available, Adding Virtual Snow Measures improves the performance by ~100%!



SnowWatch 2°°°° year

Roman Fedorov: [email protected] 23

With some irrigation <-> flooding target solutions, using SnowWatch virtual measurements is even better than using ARPA snow estimation!


Current and Future Work

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Current:• MountainWatch: real time augmented reality mobile

application• Expand tests on environmental impact

Future:• Expand area of interest and content providers• Orthophotos and new snow indexes

SnowWatch: Estimating Snow Cover from Publicly Available Images

"Complementing Snow Cover Estimation with Analysis of Web Public Images"

Software

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