I would like to discuss about "MODIS phytoplankton-ENVI".
title of this my blog post today is about Aqua/Terra MODIS image processing for detecting phytoplankton using software ENVI.
Let's start this discussion from the last word :"ENVI"
What is ENVI??
1. ENVI
We know that ENVI is great image processing and analyzing geospatial imagery.
ENVI is the premier software solution for processing and analyzing geospatial imagery used by GIS professionals, scientists, researchers, and image analysts around the world. ENVI software combines the latest spectral image processing and image analysis technology with an intuitive, user-friendly interface to help you get meaningful information from imagery.
ENVI provides us MODIS Toolkit and Ocean Color Plug-ins (previous posting : http://ajiputrap.blogspot.com/2008/12/modis-toolkit-and-ocean-color-plug-ins.html)
ENVI help us in MODIS image processing with geometric correction (bow-tie correction).
- I have uploaded in my esnips simple tutorial Aqua/Terra MODIS image processing using ENVI 4.x
http://ajiputrap.blogspot.com/2009/01/pengolahan-citra-aquaterra-modis-dengan.html
download this tutorial:
pengolahan citra modis dengan envi.pdf
-- step by step from open MODIS HDF (Level 1B), MODIS Geometric Correction (include Bow-Tie Correction), Radiometric Correction for Reflectance and Radiance Bands (use Band Math).
Another tutorial files can be downloaded in http://www.esnips.com/web/perdana09-article :
- SeaDAS_4_AquaMODIS.pdf
Tutorial Aqua/Terra MODIS image processing using SeaDAS software
- Langkah Order Citra MODIS.pdf
How to order MODIS (level 1B at Ladsweb)
2. phytoplankton
phytoplankton ??
Phytoplankton are the autotrophic component of the plankton community. The name comes from the Greek words phyton, or "plant", and πλαγκτος ("planktos"), meaning "wanderer" or "drifter".[1] Most phytoplankton are too small to be individually seen with the unaided eye. However, when present in high enough numbers, they may appear as a green discoloration of the water due to the presence of chlorophyll within their cells (although the actual color may vary with the species of phytoplankton present due to varying levels of chlorophyll or the presence of accessory pigments such as phycobiliproteins, xanthophylls, etc.).
Phytoplankton obtain energy through a process called photosynthesis and must therefore live in the well-lit surface layer (termed the euphotic zone) of an ocean, sea, lake, or other body of water.
Phytoplankton are a key food item in both aquaculture and mariculture. Both utilize phytoplankton for the feeding of the animals being farmed. In mariculture, the phytoplankton is naturally occurring and is introduced into enclosures with the normal circulation of seawater. In aquaculture, phytoplankton must be obtained and introduced directly.
References
1. ^ Thurman, H. V. (1997). Introductory Oceanography. New Jersey, USA: Prentice Hall College. ISBN 0132620723.
2. ^ "Satellite Sees Ocean Plants Increase, Coasts Greening". NASA (2 March 2005). Retrieved on 12 January 2009.
3. ^ Richtel, M. (May 1, 2007), "Recruiting Plankton to Fight Global Warming", New York Times, http://www.nytimes.com/2007/05/01/business/01plankton.html?ref=science
4. ^ Hallegraeff, G.M. (2003). Harmful algal blooms: a global overview. in Hallegraeff, G.M., Andewrson, D.M. and Cembella, A.D. (eds) 2003. Manual on Harmful Marine Microalgae. UNESCO, Paris
5. ^ G.E. Hutchinson (1961). "The paradox of the plankton". Am. Nat. 95: 137–145. doi:10.1086/282171.
6. ^ a b c d McVey, James P., Nai-Hsien Chao, and Cheng-Sheng Lee. CRC Handbook of Mariculture Vol. 1 : Crustacean Aquaculture. New York: C R C P LLC, 1993.
== source information : http://en.wikipedia.org/wiki/Phytoplankton ==
interesting question about phyto...
Where Are Phytoplankton?
The distribution of phytoplankton in the ocean have been measured by special instruments in space since 1979. The instruments, called ocean-color scanners, measure the color of the ocean. Color is proportional to the amount of chlorophyll pigments close to the surface, except in sediment-rich water very close to coasts. And the amount of chlorophyll is proportional to the amount of phytoplankton in the water. Water with great numbers of phytoplankton are green. Pure ocean water is deep navy blue.
The first ocean-color scanner, the Coastal Zone Color Scanner, was launched on the Nimbus-7 satellite in 1978. It was followed many years later by SeaWiFS (Sea-viewing Wide Field-of-view Sensor) on the Seastar satellite launched in 1997. The most recent color scanner is MODIS (Moderate Resolution Imaging Spectrometer) on the Terra spacecraft launched in 1999 and the Aqua satellite launched in 2002.
more information about distribution of phyto...read this article : Distribution of Plankton
summary from the article:
Phytoplankton are abundant in regions where:
1. Winds are able to mix nutrients up into near surface waters from deeper in the ocean, or
2. Where Ekman transports driven by the winds pulls water up from deeper in the ocean,
a. When winds blow toward the equator along west coasts of continents, and
b. When the average winds blowing at different speeds and directions cause divergence of the Ekman transports,provided a small amount iron needed by the protists is in the water.
--- MODIS (Moderate Resolution Imaging Spectrometer) on the Terra spacecraft and the Aqua satellite help us daily in monitoring or detecting phytoplankton. ---
3. MODIS (Moderate Resolution Imaging Spectrometer)
please read previously article about MODIS (http://ajiputrap.blogspot.com/search/label/MODIS)
or directly from http://modis.gsfc.nasa.gov
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Step by step Aqua/Terra MODIS (Level 1B) image processing using ENVI 4.2 software:
1. Download MODIS data level 1B 1km resolution from ladsweb...
2. Open HDF MODIS in ENVI 4.x
File -> Open External File -> Generic Format -> HDF (http://ajiputrap.blogspot.com/2008/12/modis-hdf-hierarchical-data-format.html or http://ajiputrap.blogspot.com/search/label/HDF)
3. Geometric Correction, include Bow-Tie Correction*
Bowtie Correction aims to improve image at overlapped data. Overlap occurs because there is increasing instantaneous field of view (IFOV) of 1x1 km in the lowest point (nadir). Being close to almost 2 x 5 km at the maximum scan angle is 55 degree.
After MODIS DATA geometrically corrected, then go to the next step
4. Radiometric Correction
Radiometric Correction in ENVI use Band Math (ENVI main menu, choose Basic Tool -> Band Math)
Reflectance Bands calculated for visible and thermal infrared (1 – 19 and 26 bands) with this formula:
Refb = Ref_Scaleb * (Bb - Ref_offsetsb)
where: Refb = Reflectance of band- b
Ref_Scaleb = Reflectance scale
Bb = Band -b
Ref_offsetsb = Reflectance offset band- b
-- information about reflectance scale and offset we may get it from HDF Dataset (http://ajiputrap.blogspot.com/2008/12/modis-hdf-hierarchical-data-format.html or http://ajiputrap.blogspot.com/search/label/HDF)
5. Chlorophyll-a algorithm with Band Math
After we get geometric and radiometrically corrected MODIS image, we continue to the main step : detecting Chlorophyll-a
Fitoplankton that is on a layer of light contains Chlorophyll-a useful for photosynthesis. Chlorophyll-a able to absorb a light blue and green, so it can detect the existence fitoplankton based on the ability of these Chlorophyll-a.
MODIS can help us to detecting Chlorophyll-a (Chlor-a) with formula or algorithm from Carder et al. :
Chlor-a=(10^(0.2818-(2.783*alog10(B10/B12))+(1.863*((alog10(B10/B12))^2))-
(2.387*((alog10(B10/B12))^3))))
where : B10 = Reflecance of Band 10
B12 = Reflecance of Band 12
- above is the formula of Chlor-a in Band Math of ENVI.
In addition Chlorophyll-a , we may use sea surface temperature from MODIS to get information distribution of phytoplankton in the ocean. if we combined both we may get great information...
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nice to share :)
Best Regards,
Aji Putra Perdana
