Image from TERRA
Wed, 28 Nov 2018 13:49 EST

Central Africa is still on fire a month after the October 30 image of the fire was posted. Most likely these fires are agricultural in nature.

Image from TERRA
Tue, 27 Nov 2018 10:47 EST

Just like the Woolsey Fire's scar which was highlighted on the NASA Fire page on November 16, the Camp Fire scar is visible from space in this image taken by the Terra satellite on November 26, 2018.

Image from TERRA
Thu, 15 Nov 2018 11:55 EST

In the wake of a fire, a burn scar appears which takes a long time to heal. This scar is from the Woolsey fire which has taken its toll around Thousand Oaks, California.

Year: 2015

Sensor Degradation Leads to Calibration Improvements

Changes in the MODIS sensor, not dark ice led scientists to incorrectly determine that the Greenland ice Sheet in the Arctic was darkening. These results and others led to improved calibration corrections in the Collection 6 reprocessing of Moderate Imaging Spectroradiometer (MODIS) data.

A recent study suggested that sensor degradation of the MODIS instrument on NASA’s Terra satellite was responsible for the incorrect data. Ironically, the high quality of the MODIS sensor is what initially led Arctic scientists to look for a subtle change in ice brightness. The data collected by MODIS led researchers to consider that the Greenland ice sheet was darkening from an increase in dark aerosol deposition on the snow. However, ground based measurements showed that there had been little if any change in the color of snow.

Ice darkening could have had big implications for climate researchers. Just like black asphalt absorbs radiation from the sun, resulting in a warmer surface temperature, the darkening of the ice sheet could warm the surface temperature around the snow, increasing snowmelt. This could result a shrinking Greenland ice sheet and have implications on sea level rise.

The combination of a well-understood sensor, high-quality analysis of the satellite data, and coordinated measurements at the surface led to the conclusion that a sensor artifact, a change to an image from defects or degradation of optics, was the culprit this time.

Satellites, like many scientific instruments, need to be calibrated to be able to maintain accuracy. If you’ve ever stepped on a scale and gotten a number that was far too high or too low to be accurate, you’ve been a witness to the degradation of an instrument. Scales can be fixed easily by taring, or resetting the instrument to zero when nothing is being weighed.

Fixing satellite sensor degradation, isn’t quite as easy, but is common practice. The complexity of an instrument like MODIS makes the calibration process much more difficult. Often, there are small instrument effects that are not obvious until many years of data from multiple applications indicate an issue. The dark ice example is one such case.

The vigilance of the MODIS scientists and those working with the instrument calibration led to five previous reprocessings with the sixth currently underway.. Each time the data is reprocessed, degradation of the instruments are taken into account and the data is calibrated based on data collected from other sensors on other satellites as well as from data collected on Earth. MODIS is on-board both Terra and Aqua, when data from these sensors don’t match up the data can be corrected based on data gathered on Earth.

While it may be easy to assume that an aging instrument may be less accurate, in reality the longer the data record that it collects, the more accurate the data can be through reprocessing. Just think, if Terra had only lasted it’s six year design life, instead of going on 16, this error in the data may never have been caught and accounted for in newer data collections.

Thus, while the dark ice example could be considered by some as an indication of a flaw in how satellite data are used, it is, in reality, a success story for how a community of scientists working with groups like the MODIS Characterization and Support Team are striving to get to the right answer.

References:

Sun, J., X. Xiong, A. Angal, H. Chen, A. Wu, and X. Geng, (2014) Time-Dependent Response Versus Scan Angle for MODIS Reflective Solar Bands,IEEE Transactions on Geoscience and Remote Sensing, 52 (6), 3159-3174.

Polashenski, C. M., J. E. Dibb, M. G. Flanner, J. Y. Chen, Z. R. Courville, A. M. Lai, J. J. Schauer, M. M. Shafer, and M. Bergin (2015), Neither dust nor black carbon causing apparent albedo decline in Greenland’s dry snow zone: Implications for MODIS C5 surface reflectance, Geophysical Research Letters, 42.

Atmospheric science: Arctic snow is not becoming dirtier. (2015, 29 October). Nature Research Highlights, Accessed November 25, 2015.

MOPITT Helping Shape the Future of Air Quality Monitoring

Measurements of carbon monoxide in April 2014 from the MOPITT instrument (Measurement of Pollution in the Troposphere) aboard NASA’s globally orbiting Terra spacecraft. The boxes show the observing domains for geostationary satellites and red colors indicate high levels of carbon monoxide. (©UCAR. Image courtesy Helen Worden, NCAR

Measurements of Pollution in the Troposphere (MOPITT) on NASA’s Terra satellite is being used to prove a concept in which new geostationary satellites could improve how agencies monitor and forecast air quality. Chemistry-climate model output would be combined from satellite data from a fleet of geostationary satellites.

“We think the new perspective made possible by geostationary sensors would provide data that is useful for everyday air quality forecasting, as well as for early warnings about extreme events, like the effects of wildfires,” said Helen Worden, NCAR scientist and member of the research team, according to the UCAR website.

MOPITT provides one to two measurements over a given location per day. The geostationary fleet would allow multiple measurements of certain locations per day, making it possible to track emissions over rush hour versus lower traffic times in some urban areas.

The statistical technique used to test the geostationary fleet as a proof of concept was first developed to analyze data from MOPITT, which pioneered the measurement of carbon monoxide from space.

To find out more read the full article from UCAR https://www2.ucar.edu/atmosnews/just-published/17531/tracking-air-quality-high-sky

Flooding in Iraq

20 November, 2015

turkey_Iraq_tmo_2015315

NASA Earth Observatory images by Joshua Stevens and Adam Voiland, using MODIS data from LANCE/EOSDIS Rapid Response and Landsat data from the U.S. Geological Survey.

Torrential rains in late October 2015 resulted in flooding in Iraq, prompting authorities to declare a state of emergency. Widespread power outages, overflowing sewers, and flooded streets displaced almost 84,000 people, according to news reports. The image from the Moderate Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite, featured on NASA’s Earth Observatory, shows the flooding.

To see before and after images and read the whole article visit NASA’s Earth Observatory.

 

Early Winter Weather Across North America

19 November, 2015

canada_amo_2015316 The Moderate Imaging Spectroradiometer on NASA’s Terra satellite acquired this image of Canada and the western United States in mid-November, 2015.  Snow and cold rain doused the region, bringing early winter weather and making researchers ask if this is the beginning of a wet El Niño winter. The image shows a band of snow stretching across southern Alberta and Saskatchewan.

Read the whole article on NASA’s Earth Observatory.

Dense Fog Over Europe

15 November, 2015

Europe_tmo_2015305The Moderate Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite acquired this image of dense fog in Europe. The fog appears brighter than typical clouds because the water droplets in the fog are smaller and more efficiently scatter light. The fog disrupted air travel in London and central Europe in early November 2015. The image was featured on NASA’s Earth Observatory Image of the Day.