(Images from NOAA web site).

How to use satellite data ?

River plumes modelling from Seawifs and Modis data. Florian JOSSE – August 2005

1. What are Seawifs and Modis data ? 2. What can we do with these data ? 3. Results and applications.

What are Seawifs and Modis data ? Seawifs (SEA-viewing Wide Field of view Sensor). MODIS (Moderate-resolution Imaging Spectroradiometer). The purpose of these Projects is to provide earth bio-optical data (“photography”) to the scientist community. These projects are directed by NASA by the EOS program (Earth Observation System). They are Earth reflectivity values of the sunlight. These values are measured by a satellite sensor and transmit to a ground station. This station treat the data, correct them, and provide them on the Internet for a free access to the public. (Images from Seawifs web site).

What are Seawifs and Modis data ? The result is “photography” of the Earth. These photos are composed by heights different wavelengths; all together form a true colour image. (Images from Seawifs web site).

What are Seawifs and Modis data ? Three types of Seawifs data are available: Binned data product with a global coverage. The LAC Product; a Local Area Coverage with 1 km resolution. The GAC Product; a Global Area Coverage with 4 km resolution. (Images from Seawifs web site).

What are Seawifs and Modis data ? The MODIS data available are: 44 different types of data, to study many earth characteristics. Permit scientist to work in many field: oceanography, biology, atmosphere studies, etc… Different spatial resolution: 250m, 500m, 1km. Global earth coverage in two days. Accurate and precise data, available in quantity on the Internet. (Images from MODIS web site).

What can we do with these data? Seawifs/Modis data access web site Images selection, location, clouds,.. Downloading

FTP process (downloading): It consists in a connection to an ftp web server via a web adress. Two solutions are possibles, directly with an internet navigator (Internet Explorer, Mozilla Firefox), or with an ftp client, which provide you a special interface (WS_FTP, CuteFTP). But with an Internet security system, such as the university one, it needs specific connection parameters and authorizations. After many tries, it was not possible to be connected to NASA servers. All the security systems (firewall, antispyware, etc.) not allow the connection or disconnect it after a few moment. These barrers have blocked all connections and many data could not be downloaded. It must be resolved for the future, large quantities of free data are available and can be used in many different fields. What can we do with these data?

Seawifs/Modis data access web site ENVI Exported in ASCII format And TIFF image. Select one wavelenght; 555nm (green), selection of the area, georeference it Images selection, location, clouds,.. Downloading Open with Microsoft Excel What can we do with these data?

Geolocated value point 2 points per lines ?! File 1File 2 ValueLatLong ValueLatLong What can we do with these data?

GIS: Geographical Information System. Software : ArcView 9. Database imported as X,Y,Z value points BDD (397,1071) 553 What can we do with these data?

TIFF Image Data North-South Shifting of the data ENVI bug ? Data were sending back in Excel for a direct correction of the latitude coordinate. Shift What can we do with these data?

File 1File 2 Merge One file What can we do with these data?

After parameter the legend, a first look was done on the points. A surface must be created but without the “land point”. For that a new polygon was created by digitizing the coastline, the polygon must just cover the sea area. What can we do with these data?

A grid was created for surface the area from the points. This one show river plumes as expected. A TIN (Triangulated Irregular Network) was created: this one permit a better accuracy and a no-rectangular surface than a simple interpolation. After creation, the TIN was put in a 3D view with the grid as surface. Additional elements were added for a better comprehension. What can we do with these data?

Results and applications. The results show two rivers plumes in our area: The North one is created by the Orange river. It is important, with a large influence. The South one is created by the Buffels river. Plumes can be measured and monitored: activity, size, orientation can be determined. It can be compared to precipitation, wind or current data, and see what is their influence on each others. Orange River Buffels River Mai 1998

Orange Buffels

Results and applications. A useful tool who can be link to others studies: ExampleThe West coast rock lobster What is the influence of the Orange River plume on the local biology ? Environmental studies with the impact of the river plumes on coastal biology. Physical studies with their influence on upwelling or on currents. MiningWasteIndustries

Conclusion. A method for use directly, satellite is available: a monitoring of a phenomena with bio-optical characteristics can be done (river plumes, phytoplankton bloom, algae bloom, pollution,etc.). Data can provide high resolution in term of space (250m) but also in term of time (one image every two days can be visualized). The method is easily reproductible and can be done from a simple pc with an Internet connection. All these data can be link with other studies, compute with other ones and, they can complete the knowledge. Satellite data can be use by everybody, for his own project. Many parameters can be choose, just specify your needs and download them.

Thank you to all the IOI team!