contributed by Jeffrey Gillan

MERIS, ENVISAT-MRIS

European Space Agency (ESA)

MERIS is a passive imaging sensor flying on Envisat which was launched in 2002. Similar to other sensors such as MODIS and AVHRR, it is designed to image the earth at a global and regional scale. The primary mission of MERIS is to monitor oceans and coastal areas, but has many land applications as well. Its land mission is to study the role of terrestrial surfaces in climate dynamics and biogeochemical cycles for climate change.

MERIS has 15 spectral bands within the visible and near infrared range, each capable of gathering data at a resolution of 260m across track x 300m along track. The narrow bands of MERIS make it possible to derive more accurate land cover and vegetation indices than other systems such as AVHRR.

The standard products available through MERIS include: radiance, reflectance, and two vegetation indices known as the MERIS Global Vegetation Index (MGVI) and the MERIS Terrestrial Chlorophyll Index (MTCI). Products at a reduced resolution (1040m x 1160m) can usually be obtained free of charge over the internet, while full resolution products (260m x 300m) usually have to be requested and carry a fee.

AVHRR, MODIS

_{Photo from European Space Agency}
MERIS image of Utah taken on April 27, 2008


_{Photo from European Space Agency}
A full-resolution MERIS image of a sandstorm in the Persian Gulf, taken July 1, 2008

MERIS can collect data in two modes. Reduced resolution (1040m across track x 1160m along track) is acquired and processed systematically. Full resolution (260m across track x 300m along track) is only acquired and processed on demand.

Swath width of 1150 km Scene Sizes:

• Full resolution full scene: 582 km across track x 650 km along track
• Full resolution quarter scene: 300 km across track x 334 km along track
• Reduced Resolution scene: 1165 km across track x 1300 km along track

Envisat is a polar orbiting satellite with a sun synchronous orbit. It has an altitude of 800 km above the earth and completes global coverage in 3 days.

Images from 2002 to present are available. Level 1B products are top of atmosphere radiance values Level 2 products provide geophysical information such as reflectance, and vegetation indices based on the fractional absorbed photosynthetically active radiation (FAPAR).

Products obtained over the internet are usually free of charge while new acquisitions carry some cost. Please review the product price list for more detailed information. ESA

To obtain MERIS and other Envisat data, you must register with the ESA. If you seek data that is systematically acquired and archived (reduced resolution), you can do a quick registration and get instant access. If you are interested in full resolution data, you must send a proposal requesting the acquisition, a process that can take up to 8 weeks. Use this link for registration: https://earth.esa.int/web/guest/pi-community/apply-for-data/fast-registration

Once registered, access to systematically acquired and archived data can be found through several on-line portals. https://earth.esa.int/web/guest/data-access/online-archives

If the products you seek are not available from these on-line archives, you must use the EOLI-SA tool. EOLI-SA is a java application used to visually search for and order Envisat data products. The program has to be downloaded and installed. http://earth.esa.int/EOLi/EOLi.html

Detailed information on all Envisat data products. https://earth.esa.int/web/guest/data-access/browse-data-products

Tutorial on how to access Envisat products. http://earth.esrin.esa.it/pub/ESA_DOC/ENVISAT/ENVI87a.pdf

MERIS data comes in the Envisat format which will generally have to be converted to other formats to be useful for remote sensing purposes. Please see the Software/Hardware requirements for further instructions on working with the data.

• Busler et al. (2004) used MERIS vegetation indices along with ground measurements to derive leaf area index in the Canadian prairie ecosystems.
• Klein and Menz (2005) explored the use of MERIS vegetation indices MGVI and MTCI to characterize different vegetation types in an arid region of Africa.
• Schellberg et al. (2008) looks at precision agriculture on managed grasslands. They used the MERIS Terrestrial Chlorophyll index to estimate nitrogen content in the system.

Working with MERIS data may be challenging because the default format will probably have to be converted to other formats recognized by commercial image software. Below are a few suggestions.

EnviView is a free software tool that displays MERIS and any other data from Envisat. Enviview can only carry out basic operations of visualization, therefore other commercial software packages are needed for detailed data analysis. The program will convert MERIS data to other formats that are more easily read and manipulated by image software programs. These formats include: hierarchical data format (HDF), ASCII, and binary formats. Programs such as Erdas Imagine and ENVI can read these formats. To obtain EnviView, you must send an email request to eohelp@esa.int

Basic Toolbox for Envisat AATSR and MERIS (BEAM) is an open source software program intended to compliment the functions of major commercial packages with specific tools developed to handle Envisat MERIS and AATSR products. It has the capability to read common image formats such as Geotiff. http://www.brockmann-consult.de/cms/web/beam/welcome

Still many users will find these formats cumbersome and may prefer formats such as GeoTiff. Tools for carrying out data transformations into other formats and projections can be found at: https://lpdaac.usgs.gov/tools.

• MERIS FAQ https://earth.esa.int/c/document_library/get_file?folderId=15176&name=DLFE-577.pdf
• MERIS Product Handbook http://envisat.esa.int/pub/ESA_DOC/ENVISAT/MERIS/meris.ProductHandbook.2_1.pdf
• European Space Agency https://earth.esa.int/web/guest/missions/esa-operational-eo-missions/envisat
• MERIS Wikipedia page http://en.wikipedia.org/wiki/MERIS

• Busler, J., C. Nadeau, H. When, A. Smith, and J. Freemantle (2004), Monitoring rangeland and cropland in the Canadian prairie using MERIS, proceedings of the 2004 Envisat & ERS Symposium, September 2004, Salzburg, Austria. Edited by H. Lacoste and L. Ouwehand. Published on CD-Rom, #128.1
• Klein, D. and G. Menz (2005), Vegetation assessment in East Africa using mgvi and red edge position from Envisat MERIS data, proceedings of the MERIS (A)ATSR Workshops 2005 (ESA SP-597), 26-30, September 2005 ESRIN, Frascati, Italy. Editor: H. Lacoste. Published on CD-Rom. #44.1
• Jenson, John R. (2007), Remote Sensing of the Environment: An Earth resource perspective, second edition, Prentice Hall series in geographic information science, Upper Saddle River, NJ.
• Schellberg, J., M. J. Hill, R. Gerhards, M. Rothmund, and M. Braun (2008), Precision agriculture on grasslands: applications, perspectives, and constraints, European Journal of Agronomy, Vol. 29, Iss. 2-3, pp. 59-71.

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