The Use of Satellite and Aerial Imagery, and Gps for Delineation of Ea Boundaries

Interuniversity Research Center for Sustainable Development Sapienza University of Rome, Italy

THE USE OF SATELLITE AND AERIAL IMAGERY, AND GPS FOR DELINEATION OF EA BOUNDARIES

Roberto Bianchini

2010 WORLD POPULATION AND HOUSING CENSUS PROGRAMME Regional Workshop on International Standards, Contemporary Technologies for Census Mapping and Data Processing, Minsk, Belarus, 8-12 December 2008 Interuniversity Research Center for Sustainable Development Sapienza University of Rome, Italy

Summary

1. Objectives of delineation of EA boundaries

2. Criteria for the delineation of EA boundaries

3. Main critical criterion to delineate EA boundaries

4. Principal type of maps for census operations

5. The satellite remote sensing

6. The aerial photography

7. The Global Positioning system (GPS)

8. Some conclusions

1. Objectives of delineation of EA boundaries

To support the census coverage

To support fieldwork operations

To contribute to the statistical analysis at small area level

To support sampling for statistical surveys

2. Criteria for the delineation of EA boundaries

EAs has: To cover the entire country and do not have to overlap Be consistent with the administrative division and other relevant geographic units To have boundaries easily identifiable on the ground To be of approximately equal population size in order to be covered by an enumerator during data collection (Differences in the population size may occur for urban and rural areas) To be consistent (to a larger extent) with EA boundaries used in the previous census To be large enough to guarantee data privacy

3. Main critical criterion to delineate EA boundaries

The main critical criterion is to estimate the approximately equal population size of EAs

The three methods are: - Acquisition of administrative records (or by other sources of information) - Fieldwork activities (dwellings count) - Through remotely sensed data (satellite imagery and aerial photographs), and GPS receivers

4. Principal type of maps for census operations

Small scale maps Topographic maps City maps Sketch maps High-resolution satellite images and aerial photos

4. Small scale map

4. Topographic map

4. City map

4. Sketch map

4. Manual EA delineation

4. High-resolution satellite imagery

4. Aerial photograph

5. Satellite remote sensing

The spatial resolution of a satellite image is measured by the size of a pixel on the ground. The size for commercial satellites varies from the sub-one-meter of the most popular high-resolution systems such as Quickbird and Ikonos

Indian Remote Sensing (IRS), SPOT’s panchromatic sensor and Landsat multi-spectral imagery are also considered high resolution systems which allow mapping at cartographic scales of 1:25,000 to 1:50,000 or smaller

In September 2008, the remote sensing company GeoEye launched a sensor with a pixel size of 0.41 meters panchromatic and 1.65-meter multispectral

5. Satellite remote sensing (cont.) Only some remotely sensed data products serve census work well, namely high spatial resolution data such as Geoeye (0.41), Quickbird (0.82m), Ikonos (1m), IRS (5.8m pan), Orbimage 3 and 4 (1m), and SPOT 5 (2.5m). Ikonos was launched in 1999 and Quickbird was launched in 2001.

For most census applications, 5m or better spatial resolution is needed to identify housing units. Landsat may be considered in some cases only in rural areas

On line remotely sensed data such as Google Earth, GlobeXplorer, ArcGIS Explorer, and Microsoft Virtual Earth can be used as a first test, but the image quality may not be suitable for detailed EA mapping

5. Satellite remote sensing (cont.)

High resolution satellite images show a level of geographic detail that is almost comparable to digital orthophoto maps created from air photos.

Cloud free high-resolution images may allow counts of single housing units

Aerial photography is often done on ad hoc basis, and may be more suitable for detailed surveying and mapping projects. New digital aerial photography may offer superior image quality over even high-resolution satellite imagery

5. Satellite remote sensing (cont.) Main advantages and disadvantages of high-resolution remotely sensed data:

Advantages: - High spatial resolution images offer the ability to cover large areas at a level of detail sufficient for EA delineation, provided population estimates exist for the areas delineated - Imagery can permit mapping of inaccessible areas - Usually there are no restrictions for their acquisition

Disadvantages: - Cloud may cover restricts image interpretation - Positional accuracy may be low without accurate ortho- rectification process

6. Aerial photography

Aerial photography is obtained using specialized cameras on-board low flying planes. The camera captures the image on photographic film, or digitally

Traditionally, the end products of an aerial photography project are printed photos of an area on the ground. The photogrammetrist can combine these photos to produce a seamless mosaic covering very large part of a territory

Nowadays, the most common approach is to convert the photo negative directly into a film transparency which is scanned using a very high resolution scanning device. The result is a digital image that can be displayed and processed further on a computer

6. Aerial photography (cont.)

Additional processing is required to produce orthophoto maps which combine the geometrical accuracy of a topographic map with the large detail of a photograph

The construction of digital orthophotos requires considerable expertise in photogrammetric methods, which is not usually present in a census organization

The census organization therefore needs to establish a collaborative agreement with the National Mapping Agency

6. Aerial photography (cont.)

Orthophoto maps may also support dwelling unit counts and population estimation, if is available a reliable estimate of the average number of persons per household

In a rural setting, the number of dwelling units can be determined fairly easily, while in urban settings, the number of dwellings may be more difficult to determine

Since the orthophotos are correctly georeferenced, the resulting enumeration areas will also be registered in a proper map projection with known parameters

6. Aerial photography (cont.)

Main advantages and disadvantages of high-resolution remotely sensed data:

Advantages: - Air photos provide a large amount of detail and can be interpreted visually - They usually cover the entire country

Disadvantages: - Aerial photo processing requires expensive equipment and specialized expertise - Their production is in general more expensive in comparison with high-resolution satellite imageries and requires Governmental approval

Aerial photograph (Resolution 25 cm)

Ikonos satellite imagery (Resolution 1 m)

7. Global Positioning System (GPS)

Determine current position based on signals sent by a number of satellites

GPS receivers collect the signals transmitted from more than 24 satellites—21 active satellites and three spares. The system is called NAVSTAR, and is maintained by the U.S. Department of Defense

In each area of the world, five to eight GPS satellites are within the “field of view” of a user on the earth’s surface