Violent Puffs from Krakatau. #Landsat #NASA #USGS #Earth

Violent Puffs from Krakatau

Anak Krakatau maintains a mighty and sometimes menacing presence in the Sunda Strait between Java and Sumatra, with more than 50 known periods of eruptions in almost 2,000 years. The Indonesian volcano's latest burst of activity has produced numerous plumes and lava flows in 2020, including some relatively small but notable events in April.

On April 13, 2020, the Operational Land Imager (OLI) on Landsat 8 acquired this natural-color image (OLI bands 4-3-2) of the volcano as a plume towered over the peak. The natural-color image is overlaid with the infrared signature detected by OLI of what is possibly molten rock.

"The location of the plume suggests that it is volcanic in origin," said Verity Flower, a USRA volcanologist based at NASA's Goddard Space Flight Center. Flower and colleagues use the Multi-angle Imaging Spectroradiometer (MISR) sensor on NASA's Terra satellite to measure the height of volcanic plumes and to observe the shape, size, and light-absorbing properties of the particles within plumes. "On April 12, I saw a similar feature in one of the angular MISR images with a plume-like feature above the volcano summit."

Based on the color of the plume in the image above, Flower thinks it is likely composed of mostly water vapor and gas. These small, reflective particles make a plume appear white. Conversely, larger and darker ash particles tend to look gray or brown in natural-color images.

Note the darker part of the plume extending toward the north: it appears lower in altitude than the bright, billowy part of the plume directly over the peak. "It is possible the heavier ash particles emitted are staying lower in the atmosphere and are being transported to the north by near-surface winds," Flower said. "In contrast, any water and gases within the plume, which are lighter, would be transported higher and would condense rapidly in the atmosphere."

Indonesia's Center of Volcanology and Geological Hazard Mitigation (PVMBG) reported that incandescent rock had erupted onto the volcano's surface with "insignificant intensity" in the days prior to this image.

"Anak Krakatau volcano has displayed these small eruptive bursts periodically through the last few years," Flower said. "However, it can also display more destructive activity such as tsunami-triggering eruptions."

According to the April 11 statement from PVMBG, the hazards from the volcano's recent activity included fountains of lava, lava flows, and ash rain within a radius of 2 kilometers around the crater. Thinner ash rain could extend even farther from the depending on the strength of winds. Still, the alert level remained at two on a scale of one (low) to four (high).

NASA Earth Observatory image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Kathryn Hansen.

Comments

Thermal Infrared Remote Sensing

1. Principles Thermal Infrared Remote Sensing is based on the detection of naturally emitted electromagnetic radiation from objects, rather than reflected solar energy. According to Planck's Radiation Law , all objects with a temperature above absolute zero (0 K) emit electromagnetic radiation. For Earth surface features, the peak emission lies in the Thermal Infrared (TIR) region of 3–14 μm of the electromagnetic spectrum. The amount of radiation emitted is primarily a function of surface temperature and emissivity . Sensors measure the radiant energy flux density (W/m²) , which is later converted to surface temperature using Stefan-Boltzmann's Law . 2. Radiation Properties in TIR Emissivity (ε): Ratio of radiation emitted by a surface to that emitted by a perfect blackbody at the same temperature. Natural surfaces like water (ε ≈ 0.98) have high emissivity, while bare soils and metals have lower values. Blackbody: An idealized object th...

Atmospheric Window

The atmospheric window in remote sensing refers to specific wavelength ranges within the electromagnetic spectrum that can pass through the Earth's atmosphere relatively unimpeded. These windows are crucial for remote sensing applications because they allow us to observe the Earth's surface and atmosphere without significant interference from the atmosphere's constituents. Key facts and concepts about atmospheric windows: Visible and Near-Infrared (VNIR) window: This window encompasses wavelengths from approximately 0. 4 to 1. 0 micrometers. It is ideal for observing vegetation, water bodies, and land cover types. Shortwave Infrared (SWIR) window: This window covers wavelengths from approximately 1. 0 to 3. 0 micrometers. It is particularly useful for detecting minerals, water content, and vegetation health. Mid-Infrared (MIR) window: This window spans wavelengths from approximately 3. 0 to 8. 0 micrometers. It is valuable for identifying various materials, incl...

Regional Geography, Systematic Geography, Idiographic, Nomothetic, Inductive and Deductive Approaches

T wo major ways of studying Geography : the Regional Approach and the Systematic Approach . It also explains the related ideas of idiographic vs. nomothetic and inductive vs. deductive reasoning , especially in the context of the Hartshorne–Schaefer debate . 1. Regional Geography: “All About One” Regional Geography studies one particular region in detail . A region is an area that has some degree of homogeneity (sameness) within its boundary but is also unique or different from other regions . For example, if we study Palakkad District , we may study: Relief and drainage Climate Soil Vegetation Agriculture Population Occupation Economy Culture Political characteristics The purpose is to understand the complete geographical personality of Palakkad and the relationships among its different features. Key concepts Region: A geographical area with identifiable characteristics and boundaries. Homogeneity: Si...

Radar image. Polarization in Remote Sensing

L band radars operate on a wavelength of 15-30 cm and a frequency of 1-2 GHz. L band radars are mostly used for clear air turbulence studies. S band radars operate on a wavelength of 8-15 cm and a frequency of 2-4 GHz. Because of the wavelength and frequency, S band radars are not easily attenuated. . Polarization refers to the direction of travel of an electromagnetic wave vector's tip: vertical (up and down), horizontal (left to right), or circular (rotating in a constant plane left or right). . a synthetic aperture radar (SAR) for high-resolution imaging. a radar altimeter, to measure the ocean topography. echo amplitude a wind scatterometer to measure wind speed and direction. Other types of radars have been flown for Earth observation missions: precipitation radars such as the Tropical Rainfall Measuring Mission, or cloud radars like the one used on Cloudsat. . RISAT-1 (SAR, ISRO India, 2012) RORSAT (SAR, Soviet Union, 1967-1988) Seasat (SAR, altimeter, scatterometer, US, 19...

Discrete Detectors and Scanning mirrors Across the track scanner Whisk broom scanner.

Multispectral Imaging Using Discrete Detectors and Scanning Mirrors (Across-Track Scanner or Whisk Broom Scanner) Multispectral Imaging: This technique involves capturing images of the Earth's surface using multiple sensors that are sensitive to different wavelengths of electromagnetic radiation. This allows for the identification of various features and materials based on their spectral signatures. Discrete Detectors: These are individual sensors that are arranged in a linear or array configuration. Each detector is responsible for measuring the radiation within a specific wavelength band. Scanning Mirrors: These are optical components that are used to deflect the incoming radiation onto the discrete detectors. By moving the mirrors, the sensor can scan across the scene, capturing data from different points. Across-Track Scanner or Whisk Broom Scanner: This refers to the scanning mechanism where the mirror moves perpendicular to the direction of flight. This allows for t...

Vineesh V, Geography

Search This Blog