aeromodel to fill the lack in satellite images

Use of aeromodel

to complete the lack in satellite images.

Bernard LORTIC (IRD) - Zelealem Addis (ECSC)

The Institute of Urban Development studies (part of ECSC) is working on and teaching urban planning. Each year, the students have to renew and to propose a « new » master plan for a little city. In order to perform that, since the year 2008, we use two “new” technologies : GPS and satellite images,according with the method proposed by B. Lortic (IRD). We use GPS data in order to georeference the satellite image and plot it on a screen display of the images the streets, the blocks, the parcels, the buildings and so on. The process is described in :first_approach/index_english.html

Some difficulties to use only satellite images (Ikonos, Quick bird, Komsat2 or Woldview)
Even the whole process seems very efficient, it should occur two difficulties to perform perfectly the updated map.
First problem : Clouds. We use images taken of the visible part of radiometric spectrum. Theses images look like classical photography and correspond with our vision. Obviously any cloud mask the earth surface. Practically it not so easy to get all the area absolutely without cloud. The the resellers companies (Digital globe, GeoEyes or Spot image) doesn't certify the absence of cloud. If you ask a new image with order process, first you have to pay and you cannot refuse the image if there is no more of 20% of clouds. It is because, even with a very good weather they are, very often, some little cumulus clouds. We can give two examples :

Some difficulties to use only satellite images (Ikonos, Quick bird, Komsat2 or Woldview)

Even the whole process seems very efficient, it should occur two difficulties to perform perfectly the updated map.

First problem : Clouds. We use images taken of the visible part of radiometric spectrum. Theses images look like classical photography and correspond with our vision. Obviously any cloud mask the earth surface. Practically it not so easy to get all the area absolutely without cloud. The the resellers companies (Digital globe, GeoEyes or Spot image) doesn't certify the absence of cloud. If you ask a new image with order process, first you have to pay and you cannot refuse the image if there is no more of 20% of clouds. It is because, even with a very good weather they are, very often, some little cumulus clouds. We can give two examples :


In this very good image of Debre Markos (only 1% cloud cover) we have a little cloud in the north of the town. For this little part of the city, the students worked with Total station and decametres. It needs time and doesn't give so good results.	In this good image of Weldiya exist however a little cloud and its shadow in the south of the town. It is not very important, but it should be part of possible extension area.

We can find some others problems, especially with the great speed of changing in Ethiopia : In case of Debre Markos, even we worked with a « recent » image, we lost half of the university buildings that was built up during the six last months.

Another problem is due to the image resolution of the “new” very hight resolution satellites. Pixels have a size between 50 cm and 1 meter, that is not sufficient to draw properly and distinctly all the buildings in the old parts of the city. Case of a new city : Hossaena.


For 95% of the buildings it is easy to draw the individual houses........	But in the old part of the city (in this case, around the old market) it can be very difficult to individualize each building. The shape and the boundaries of each one can be not obvious.

An alternative : remote control unmanned little planes.
In order to solve these problems we can use aerial photographies from a little plane like Cessna ( cf : ) or ultra light plane with motor, but the both are not so easy to use and manage : it is costly and the distances from Addis Ababa can be important. That's means in case of bad weather conditions a hight coast or a bad result. So we propose to use engines that are considered as « toys ». With the same way that we use “touristic” GPS, we propose to use the aeromodel engines of the brand Robbe or Graupner. These planes are generally used for fun. The two brands sail car, wind boats, motors boats, glides, planes and helicopters with “low” cost because they are “toys”. Obviously, we will not attempt to get the whole cover of a town with this little toys. The instability of the plane s doesn't allow a good mission in order to make the whole cover of a town. The aim is more to get some little parts and after to process a patchwork, with a mosaicking process, filling the lack of the main source (Ikonos or Quickbird image).
We propose to use two different models : 1 glider and 1 para glider. The both are driven by remote control radio. The both are a flight range of 500 meters, no much more because we have to use a visual control. With a glider, we can use a plane of 3 meters wingspread that is sufficient for a good control. The para gliders are smaller :1,20 meters and it can be useful only on very local area, only for a block of dwelling. Putting a little camera inside the engine we are able to take aerial photographies at the hight of 200 or 400 meters. We can check the approximate altitude with a little telemeter.

An alternative : remote control unmanned little planes.

In order to solve these problems we can use aerial photographies from a little plane like Cessna ( cf : ) or ultra light plane with motor, but the both are not so easy to use and manage : it is costly and the distances from Addis Ababa can be important. That's means in case of bad weather conditions a hight coast or a bad result. So we propose to use engines that are considered as « toys ». With the same way that we use “touristic” GPS, we propose to use the aeromodel engines of the brand Robbe or Graupner. These planes are generally used for fun. The two brands sail car, wind boats, motors boats, glides, planes and helicopters with “low” cost because they are “toys”. Obviously, we will not attempt to get the whole cover of a town with this little toys. The instability of the plane s doesn't allow a good mission in order to make the whole cover of a town. The aim is more to get some little parts and after to process a patchwork, with a mosaicking process, filling the lack of the main source (Ikonos or Quickbird image).

We propose to use two different models : 1 glider and 1 para glider. The both are driven by remote control radio. The both are a flight range of 500 meters, no much more because we have to use a visual control. With a glider, we can use a plane of 3 meters wingspread that is sufficient for a good control. The para gliders are smaller :1,20 meters and it can be useful only on very local area, only for a block of dwelling. Putting a little camera inside the engine we are able to take aerial photographies at the hight of 200 or 400 meters. We can check the approximate altitude with a little telemeter.

Some documents about Paraglider from Graupner (Gernany)

Michael Muller, Germany

Some examples of images from non- professional sportsmen in Germany.

Some documents about Glider from Grobbe (Germany)

We choose this model because of its size : almost 3 meters. This is a condition to get a quite good stability.


Camera.
We will use some little numerical camera : EXAMPLE for the best today : Nikon Coolpix S700 : Price : 400 euros Size : 89x54x23 mm Weight : 130 gr Resolution : 4000x3000 pixels. According with our resources, we can choose something cheaper.

The disadvantages and advantages of remote control little planes.
- Lack of stability. The little size of the engine can involve some difficulties to get an exact vertical image. In fact, we think it should be quite better than the actual very hight resolution satellite : that ones take not only vertical image but, very often, image between -25° and +25° of incidence. - Difficulties to manage a remote control plane (even it is very easy to pilot a para-glider). That involved a time of learning; almost 2 fly hours; that means some days. It should be more for a glider 3D as the SkyWind 280. - Availability . The satellites have a repetitiveness of almost 2 weeks. That means that for a define city, if we got an image the first of September, we can't expect another flight, another image, before the 15^th of September, that reduce a lot the possibility of satellite system. In the contrary, with a remote control plane, we have just to wait good weather conditions (no wind) and we can operate within 30 minutes. It is possible to take 3 or 4 set of images per day.

The disadvantages and advantages of remote control little planes.

- Lack of stability. The little size of the engine can involve some difficulties to get an exact vertical image. In fact, we think it should be quite better than the actual very hight resolution satellite : that ones take not only vertical image but, very often, image between -25° and +25° of incidence.

- Difficulties to manage a remote control plane (even it is very easy to pilot a para-glider). That involved a time of learning; almost 2 fly hours; that means some days. It should be more for a glider 3D as the SkyWind 280.

- Availability . The satellites have a repetitiveness of almost 2 weeks. That means that for a define city, if we got an image the first of September, we can't expect another flight, another image, before the 15^th of September, that reduce a lot the possibility of satellite system. In the contrary, with a remote control plane, we have just to wait good weather conditions (no wind) and we can operate within 30 minutes. It is possible to take 3 or 4 set of images per day.

How to use these new images.
After the flight, we just download the pictures from the camera to the computer. This images are not different than a satellite image and can be used exactly with the same process (first georeferencing, after digitizing).

Refences :
Warner, Graham R.W., Read R.E. ; “Small format aerial photography”; ISBN 1-870325-56-7 Fleming, Dixon,; “Basic guide to small format hand held aerial photography” Petrie, “Orthophotomaps”.

Refences :

Warner, Graham R.W., Read R.E. ; “Small format aerial photography”; ISBN 1-870325-56-7

Fleming, Dixon,; “Basic guide to small format hand held aerial photography”

Petrie, “Orthophotomaps”.

Requirements :
1) Permission to use the wavelength a remote control with 41 Mhz . 2) Permission to “flight” in an adequate training place near Addis Ababa. (M. Lortic and some few students of IUDS) 3) Permission to flight and to take some photographies, in some little cities where we are working as Debre Birhan, Kombolcha, Hossaena or others.

Requirements :

1) Permission to use the wavelength a remote control with 41 Mhz .

2) Permission to “flight” in an adequate training place near Addis Ababa. (M. Lortic and some few students of IUDS)

3) Permission to flight and to take some photographies, in some little cities where we are working as Debre Birhan, Kombolcha, Hossaena or others.