August 4th, 2014
Terra MODIS True Color Imagery (click to play animation)
As happened in 2011, an algae bloom is ongoing over Lake Erie. The current bloom has contaminated at least one water intake for Toledo, Ohio’s municipal water supply with microcystin, a cyanobacter that when ingested can damage the liver and nauseate people. (There is also significant danger to pets). A series of true-color images (from 4 July, 1 August and 4 August) taken from the MODIS Today website, above, (combining visible channels at 0.6465 µm [red], 0.5537 µm [green] and 0.4656 µm [blue]) shows changes in the water color over the past month. (Image Source: MODIS Today) Some changes are apparent over western Lake Erie that are associated with the toxic bloom.
The algal growth is more readily apparent in the false-color imagery below. This red/green/blue image is constructed with 2.1143 µm imagery as ‘red’, 0.8567 µm imagery as ‘green’ and 0.6465 µm imagery as ‘blue’. The animation including scenes from 4 July, 1 August and 4 August shows dramatic growth between 1 and 4 August. Near-infrared channels — such as 0.8567 µm — are sensitive to energy reflected by algae.
Terra MODIS True Color Imagery (click to play animation)
A series of True-Color images for six days this Spring/Summer is here. The increase in algae in the western part of Lake Erie is apparent, but it seems that the outbreak this year is less wide-spread than the outbreak in October of 2011. A series of False-Color images is here.
[Update, 5 August 2014: Toledo’s water supply has been deemed safe to drink]
May 28th, 2013
Suomi NPP VIIRS 1.61 Âµm “snow/ice discrimination channel” images
A sequence of AWIPS images of Suomi NPP VIIRS 1.61 Âµm near-IR “snow/ice discrimination channel” data covering the period from 13:47 UTC on 27 May to 23:24 UTC on 28 May 2013 (above) showed the effects of ice jam flooding along the Yukon River in the vicinity of Galena, Alaska (station identifier PAGA). In addition to snow and ice, water is also a strong absorber at the 1.61 Âµm near-IR wavelength — so it appears darker on the images. This dark signature of water inundation can be seen increasing in areal coverage during that 1.5 day period. This flooding forced the evacuation of aruond 300 residents of Galena, as many homes were extensively damaged by the flooding.
A comparison of Suomi NPP VIIRS 0.64 Âµm visible channel, 0.86 Âµm “land/water discrimination channel”, and 1.61 Âµm “snow/ice discrimination channel” images at 21:43 UTC on 28 May (below) showed that the Yukon River downstream of Galena was still snow/ice covered (appearing brighter white on the 0.64 Âµm and 0.86 Âµm images). Meanwhile, the darker signature of floodwaters near and upstream of Galena was evident to some extent on the 0.86 Âµm image, but was even more pronounced on the 1.61 Âµm image. The Yukon River ice jam flooding in the Galena area occurred about a week after similar ice jam floding occurred much farther upstream in the Fort Yukon area.
Suomi NPP VIIRS 0.64 Âµm visible channel, 0.86 Âµm land/water discrimination channel, and 1.61 Âµm snow/ice discriminatioon channel images
May 20th, 2013
Suomi NPP VIIRS 1.61 Âµm near-IR “snow/ice channel” images
A comparison of AWIPS images of Suomi NPP VIIRS 1.61 Âµm “snow/ice discrimination channel” data from 19 May and 20 May 2013 (above) revealed the areal extent of flooding along the Yukon River upstream of the Fort Yukon (station identifier PFYU) area in northeastern Alaska. Both ice and water are strong absorbers at the 1.61 Âµm wavelength, so they appear very dark on the images. The flooding along the Yukon River began as a surge of ice and water moved through the Eagle, Alaska (station identifier PAEG) area on 17 May, then continued downstream to produce major flooding in the Circle, Alaska area on 19 May (Circle is located about halfway between PAEG and PFYU). An ice jam had formed about 12 miles upstream of Fort Yukon, which then impounded the flow of ice and water that had flooded Circle, leading to the increased flooding seen upstream of Fort Yukon on 20 May.
A comparison of Suomi NPP VIIRS 0.64 Âµm visible channel, 0.86 Âµm “land/water discrimination channel”, and 1.61 Âµm “snow/ice discrimination channel” at 20:52 UTC on 20 May (below) showed how the 0.86 Âµm and 1.61 Âµm images can be used to identify the darker flooded portions of the Yukon River that are not apparent on the 0.64 Âµm visible image.
Suomi NPP VIIRS 0.64 Âµm visible channel, 0.86 Âµm “land/water” channel, and 1.61 Âµm “snow/ice channel” images
April 21st, 2013
Total observed precipitation during the 07-21 April 2013 period
The middle part of April 2013 brought periods of very heavy rainfall to portions of Illinois and the Upper Midwest region, with many areas receiving 5-7 inches of rainfall. A map of the 14-day total observed precipitation during the 07-21 April period (above) shows the widespread distribution of the heavy rainfall, which was 4-5 inches above normal and 300-400% of normal at many locations for this time of the year. Additional information can be found at the NWS Chicago and NWS Lincoln sites.
The effect of this heavy rainfall was very apparent in a before (05 April) and after (21 April) comparison of 250-meter resolution MODIS false-color Red/Green/Blue (RGB) images from the SSEC MODIS Today site (below) — obvious changes can be seen in the width of sections of the Illinois River (which runs fron northeast through southwest across the center of the images) and many of its tributaries. 138 river gauges were reporting moderate to major flooding levels on 21 April.
MODIS false-color Red/Green/Blue (RGB) images from 05 April and 21 April 2013
AWIPS image comparisons of the standard 0.64/0.65 Âµm visible channel with the corresponding 0.86 Âµm visible channel from the VIIRS and MODIS instruments (below) show that the 0.86 Âµm imagery can be useful for helping to monitor the areal coverage of significant water inundation following heavy rainfall events such as this. Rivers, lakes, and flooded areas show up as darker features on the 0.86 Âµm images.
Suomi NPP VIIRS 0.64 Âµm visible and 0.86 Âµm visible channel images
MODIS 0.65 Âµm (Band 1) visible channel and 0.86 Âµm (Band 2) visible channel images