urban mapping in gis

8/11/2019 Urban Mapping in Gis

1/28

URBAN MAPPINGHIGH-RESOLUTION SATELLITEIMAGERY &

AERIAL PHOTOGRAPHY (IKONOS 2 & AVIRIS)

Gianni Gorgoglione


2/28

Introduction

SATELLITES & AIRBORNE

IMPERVIOUS SURFACES ADVANTANGES & DISAVANTAGESATELLITE IMAGE PROCESSING

RESULTSDISCUSSION/QUESTIONS


3/28

IKONOS SATELLITE VS AIRBORNE


4/28

HIGH-RESOLUTION SATELLITEIMAGERY

Max panchromatic resolution of 0.5 m per pixel

Max multispectral resolution of 4 m per pixelSwath width 13-70 km

IKONOS 2 Swath -11 km 11 km (singlescene)Orbit Height 681-709 kmRevisit rate for IKONOS is 3 to 5 days off-nadir and 144 days for true-nadir

https://earth.esa.int/web/guest/missions/3rd-party-missions/current-missions/ikonos-2


5/28

AIRBORNE PHOTOGRAPHY

AVIRISMaximum spatial resolution up to 2.5 cm per pixelER-2 jet or Twin Otter GRC airplanesflies at approximately 20 km above sea level (Er-2 jet)Whisk broom scanning

http://aviris.jpl.nasa.gov/aviris/index.html


6/28


AVIRISvisibility (on a clear day about 80km-100km)224 contiguous spectral channels (also called bands) with

wavelengths from 400 to 2500 nanometers (nm) VIS-NIR-SWIR



7/28


AVIRISER-2 (20km above the ground) each pixel produced by theinstrument covers an area approximately 20 meters

diameter on the ground

Ground swath about 11 kilometers wide



8/28


AVIRISTwin Otter (4km above the ground), each ground pixel is 4m

square, and the swath is 2km wide



9/28


AVIRIS STORAGE CAPACITY

140 Megabytes (MB) for every 512 scans (or lines) of data. Each512 line set of data is called a "scene", and corresponds to an area

about 10km long on the ground A full AVIRIS disk can yield about 76 Gigabytes (GB) of data perday (Last Updated: October 30, 2007)



10/28


AVIRISPHOTOGRAPHY EXAMPLE

GULF COAST OIL SPILL 2010



11/28

SATELLITE & AERIALPHOTOGRAPHY


12/28

SATELLITE & AERIALPHOTOGRAPHY


13/28

IMPERVIOUS SURFACES DEFINITION

Any materials that water cannot infiltrate and is primarily associated with human activities andhabitation through construction of transportationand buildings

(Slonecker 2001, Bauer 2004)


14/28

IMPERVIOUS SURFACES

Ikonos composite image

Bright buildings roofs highreflectanceRoads or dark roofs lowreflectance (They absorb major part ofvisible light, near IR and shortwave IR)


15/28

IMPERVIOUS SURFACES

Different kind of roof material havedifferent reflectance

Tiles, metal sheet roof, asphalt, wood,


16/28

IMPERVIOUS SURFACES

It could be more complicated!

metal sheet roof

More complicated?


17/28


AVIRIS

http://omsjena.geogr.uni-jena.de/~c5hema/pub/rse04_heroldetal.pdf


18/28

ADVANTAGES & DISAVANTAGES

Geometric Distortions of AerialMost of aerial photo provides aperspective view. Perspective

views give a geometricallydistorted image of the Earthsurface. Distortion in aerialphotographs comes primarilyfrom two sources: camera tiltand terrain variation.


19/28


Geometric Distortions of AerialGeometric distortion on anaerial photograph due to

camera tilt


20/28


Geometric Distortions of Aerial

Geometric distortion on anaerial photograph due toterrain variation


21/28



Advantages DisadvantagesMaximum spatial resolution up to 2.5 cm perpixel

Need of bigger space storage

Weather condition Airplanes can takephotographs where Satellite sensors cannot workproperly

The aircraft body is tilted in order to take slantingpictures because position can vary

Older archive of imagery collection from the past.While new satellite observations started in 1972

Time consuming process. However, now moderncameras can capture strip of data and not only aframe.

Easy maintenance for technical service

Installation of multi spectral cameras that worksimultaneously

Lower cost


22/28



Advantages DisadvantagesPanchromatic images with a spatial resolutionof 1 m or better.

Lower resolution than aerial photography.Maximum spatial resolution is circa 50 cm perpixel.

Better opportunities for slanting observationthan perpendicular observation

One critical step is to extract dark impervioussurface areas and shadowed impervioussurfaces, which are often confused with waterand shadows cast by tree crowns.

Large coverage area, short revising time The tall buildings-cast shadows and treecrowns in the high spatial resolution imageryrepresent a problem for extracting impervioussurfaces. They look like water or wet lands.

Speed. Location of satellite can move fasterthan aerial image. Satellite can take a largeramount of data that means less time.

Weather condition can determinate the resultof satellite imagery

Difficult to change cameras onboard

Higher cost


23/28

SATELLITE IMAGE PROCESSING

DECISION TREE CLASSIFICATION

METHOD (DTC) is a Algorithmic calculationwith purpose to classify and predictcategories from a set of trainingcases/objects and their attribute values


24/28

Method applied on urban mapping from Ikonosimagary processing:

1) Creation of 3 classifiers for 3 levels reflectance

2) NDVI index to separate vegetation from Impervioussurfaces (IS)

3) VIS for high and medium reflectance for IS,NIR for low reflectance for IS

4) Unsupervised ISODATA classification (sinceDTC cannot detect clearly SHADOWS AND WATER


DTC


25/28


Figure from Lu, Dengsheng and Weng, Qihao(2009)'Extraction of urban impervioussurfaces from an IKONOS image',International Journal of Remote Sensing


26/28


a) Maximum Likelihood Classification MLC (b) DTC on IKONOS data


27/28

RESULTS

Most accurate method to extract impervioussurfaces is the combination of non-parametricdecision tree classification and unsupervisedISODATA classifier (Dengsheng Lu & Qihao Weng ,2009)Higher resolution and more flexibility of aerialphotography is still an advantage for urban

mapping despite the higher cost Aerial photography and satellite imagery arecomplementary


28/28

Questions/Discussions

The increasing of technology of digital camerasmake more complex decision above whichdevice is more suitable for imagery productiondepending on the circumstancesIs it really possible to decide a priori whichmethod is more accurate?

urban mapping in gis

Documents