These images were acquired by the geostationary NOAA GOES 9, 10 and
12 weather satellites and have been processed here at the University of Hawaii by
researchers at the Hawaii Institute of Geophysics and Planetology. By the time that
we process and display these images, the data are usually 10-30 minutes old. Since
the satellites acquires images every 15 minutes, we are updating our images at that
frequency, permitting near real-time observations of hot spots and cloud motions.
Most of our images are 1000 x 1000 pixels in size, with pixels that are about 1
km across. The exceptions are the image of the Island of Hawaii, which is 440 x 400,
with 0.5 km pixels, the image of the Hawaiian Island chain, which is 800 x 500 x 1.0 km,
and images of the Galapagos, Western Africa, and Northern New Zealand, which are 500 x 500 x 1.0
The images for each site have been extracted from a much larger image which covers most of the Earth's hemisphere visible to each GOES satellite. Since the GOES satellites remain in geostationary orbit (remain in the same location) above the Western Hemisphere, all of our sites are limited to areas within the 3 major areas; Eastern Asia and the Western Pacific, the Central and Eastern Pacific, and North, Central and South America.
Our image products are based on data collected in three wavebands. Band 1 data are collected in the visible portion of the spectrum, at a waveband of 0.55 to 0.75 µm, and then converted to albedo, a measure of reflectance. The resolution of Band 1 is about 1 km. Band 2 data are collected in the mid-infrared portion of the spectrum, at a waveband of 3.80 to 4.00 µm. The resolution of Band 2 is about 4 km. Band 4 data are collected in the thermal-infrared portion of the spectrum, at a waveband of 10.20 to 11.20 µm. The resolution of Band 4 is about 4 km.
The label under each image gives the Hawaii Standard date and time at which we processed these images, as well as the satellite name, date and time (UT) at which the satellite acquired the image data, and the name of the image.
Thu Feb 10 09:21:37 2000 20000210.1200.g10.rgb indicates that the image was processed here at the University of Hawaii on Thursday, February 10, 2000 at 9:21 am Hawaii Standard time.
Thu Feb 10 09:21:37 2000 20000210.1200.g10.rgb indicates that the data was acquired on 02/10/2000, at 12:00 am UT.
Thu Feb 10 09:21:37 2000 20000210.1200.g10.rgb indicates that the data was acquired by the GOES 10 satellite.
Thu Feb 10 09:21:37 2000 20000210.1200.g10.rgb indicates that the image type is "rgb".
The five image products that we produce are outlined below. Use caution when interpreting these images. The strong temperature difference between land, water and clouds may generate false hotspots along coastlines and cloud egdes. Additoinally, daytime solar reflection off of land, water or clouds may generate scattered false hotspots.
The first image is a map the site showing the relationship between hotspots, roads, towns, and landforms. Areas that might be thermally interesting (hotspots) are highlighted in yellow and surrounded by a green border.
The second image is a false color image which combines data from Band 1, Band 2, and Band 4. The red band of the image is mapped to the level of Band 2 normalized by the mean Band 2 value for the whole image. The green band is a scaled representation of Band 1 (visible). The blue band is mapped to an inverted Band 4. The colder something is, the bluer it is. This color scheme results in daytime images that appear somewhat real (ocean is blue, clouds are whitish, land is grey or green. During the night, the land will turn blue as it cools, while the ocean will appear red because it is still warm. Hotspots in this image appear redish.
The third image is produced from Band 1 data. Since Band 1 is a measure of albedo, this image allows cloud, land, and water to be distinguished on the basis of their reflectance. Clouds are evident as light areas due to their high albedo. Land and water appear as darker areas owing to their lower albedo. At night this image is dark and shows nothing because there is no reflected sunlight to be detected. This image has been stretched to emphasize the detail at low albedo levels.
The fourth image is similar to the RGB image. The main difference being that the green band is mapped to probability, as defined below. This means that while hot areas will be red and colder areas will be blue, true hotspots will show up as bright yellow.
The fifth image is a tool that is designed to determine areas of thermal interest. It is the defined as Band 2 minus Band 4 divided by Band 2 plus Band 4. During the day, the Band 2 value is corrected for reflected light by subtracting a weighted Band 1. This means that anything that is thermally bright, and has a large difference, and is not visibly bright has the best chance of being thermally interesting. Small hot spots are particularly easy to spot in this image.
In addition to the images, tables of statistics are calculated for the image as a whole, and
sometimes for select areas of the image. The values in these "log" files are as follows:
Band 1 Albedo: Peak, Mean and Standard Deviation
Band 2 Radiance: Peak, mean and Standard Deviation
Band 4 Radiance: Peak, mean and Standard Deviation
Band 2 Radiance, corrected for reflectance and cooling with altitude: Peak, mean and Standard Deviation
Band 4 Radiance, corrected for cooling with altitude: Peak, mean and Standard Deviation
Corrected Band 4 minus band 2 Radiance: Peak, mean and Standard Deviation
Probability Index: Peak, mean and Standard Deviation
Total Pxiel Count
Hot Pixel Count
Saturated Pixel Count
Further information about the GOES satellites is available from the NOAA Satellite Information System at: http://psbsgi1.nesdis.noaa.gov:8080/EBB/ml/nic00.html.
|Software development by Andy Harris, Eric Pilger, and Harold Garbeil, Hawaii Institute of Geophysics and Planetology.|
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GOES 9/10/12 Hotspot Images
Hawai'i Institute of Geophysics and Planetology,
School of Ocean and Earth Science and Technology,
University of Hawai'i
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