Feng-Chi Hsu

VIIRS Nightfire: Satellite Pyrometry at Night

The Nightfire algorithm detects and characterizes sub-pixel hot sources using multispectral data collected globally, each night, by the Suomi National Polar Partnership (NPP) Visible Infrared Imaging Radiometer Suite (VIIRS). The spectral bands utilized span visible, near-infrared (NIR), short-wave infrared (SWIR), and mid-wave infrared (MWIR). The primary detection band is in the SWIR, centered at 1.6 μm. Without solar input, the SWIR spectral band records sensor noise, punctuated by high radiant emissions associated with gas flares, biomass burning, volcanoes, and industrial sites such as steel mills. Planck curve fitting of the hot source radiances yields temperature (K) and emission scaling factor (ESF). Additional calculations are done to estimate source size (m2), radiant heat intensity (W/m2), and radiant heat (MW). Use of the sensor noise limited M7, M8, and M10 spectral bands at night reduce scene background effects, which are widely reported for fire algorithms based on MWIR and long-wave infrared. High atmospheric transmissivity in the M10 spectral band reduces atmospheric effects on temperature and radiant heat retrievals. Nightfire retrieved temperature estimates for sub-pixel hot sources ranging from 600 to 6,000 K. An intercomparison study of biomass burning in Sumatra from June 2013 found Nightfire radiant heat (MW) to be highly correlated to Moderate Resolution Imaging Spectrometer (MODIS) Fire Radiative Power (MW).

DMSP-OLS Radiance Calibrated Nighttime Lights Time Series with Intercalibration

The Defense Meteorological Satellite Program-Operational Linescan System (DMSP-OLS) stable lights products are made using operational OLS data collected at high gain settings, resulting in sensor saturation on brightly lit areas, such as city centers. This has been a paramount shortcoming of the DMSP-OLS stable lights time series. This study outlines a methodology that greatly expands the dynamic range of the OLS data using observations made at different fixed-gain settings, and by incorporating the areas not affected by saturation from the stable lights product. The radiances for the fixed-gain data are computed based on each OLS sensor’s pre-flight calibration. The result is a product known as the OLS radiance calibrated nighttime lights. A total of eight global datasets have been produced, representing years from 1996 to 2010. To further facilitate the usefulness of these data for time-series analyses, corrections have been made to counter the sensitivity differences of the sensors, and coefficients are provided to adjust the datasets to allow inter-comparison.

Automatic Boat Identification System for VIIRS Low Light Imaging Data

The ability for satellite sensors to detect lit fishing boats has been known since the 1970s. However, the use of the observations has been limited by the lack of an automatic algorithm for reporting the location and brightness of offshore lighting features arising from boats. An examination of lit fishing boat features in Visible Infrared Imaging Radiometer Suite (VIIRS) day/night band (DNB) data indicates that the features are essentially spikes. We have developed a set of algorithms for automatic detection of spikes and characterization of the sharpness of spike features. A spike detection algorithm generates a list of candidate boat detections. A second algorithm measures the height of the spikes for the discard of ionospheric energetic particle detections and to rate boat detections as either strong or weak. A sharpness index is used to label boat detections that appear blurry due to the scattering of light by clouds. The candidate spikes are then filtered to remove features on land and gas flares. A validation study conducted using analyst selected boat detections found the automatic algorithm detected 99.3% of the reference pixel set. VIIRS boat detection data can provide fishery agencies with up-to-date information of fishing boat activity and changes in this activity in response to new regulations and enforcement regimes. The data can provide indications of illegal fishing activity in restricted areas and incursions across Exclusive Economic Zone (EEZ) boundaries. VIIRS boat detections occur widely offshore from East and Southeast Asia, South America and several other regions.

Exploring and estimating in-use steel stocks in civil engineering and buildings from night-time lights

Steel is the most widely used metal in the world, and numerous studies have investigated its stock and flow. Two basic methods for analysing material flow and accounting for stock are the top-down and bottom-up approaches. Their applicability, however, largely depends on data availability. To overcome this limitation, we have contemplated using satellite imagery as a proxy for missing data. In a previous study, we confirmed the correlation between night-time light radiance and civil engineering/building in-use steel stocks in Japan. In this study, the scope of the investigation was expanded to a global scale, examining correlations in different regions of the world. We found that night-time light radiance and in-use steel stocks have region-specific linear correlations, which are influenced by construction styles, which in turn depend on climate, seismic activity, cultural preferences, etc. The results were then applied to countries in the various regions whose in-use steel stocks were previously unreported. This technique produced an estimate of the global civil engineering/building in-use steel stock of around 9 × 109 tonnes (9 Gt), with 1.24 Gt being previously unreported. As a further step, this study shows the spatial distribution of civil engineering/building in-use steel stock in each region.

Long-wave infrared identification of smoldering peat fires in Indonesia with nighttime Landsat data

Smoldering peat fires in Indonesia are responsible for large quantities of trace gas and particulate emissions. However, to date no satellite remote sensing technique has been demonstrated for the identification of smoldering peat fires. Fires have two distinct combustion phases: a high temperature flaming and low temperature smoldering phases. The flaming phase temperature is approximately twice that of the smoldering phase. This temperature differential results in a spectral displacement of the primary radiant emissions of the two combustion phases. It it is possible to exploit this spectral displacement using widely separated wavelength ranges. This paper examines active fire features found in short-wave infrared (SWIR) and long-wave infrared (LWIR) nighttime Landsat data collected on peatlands in Sumatra and Kalimantan. Landsat 8s SWIR bands are on the leading edge of flaming phase radiant emissions, with only minor contribution from the smoldering phase. Conversely, Landsat 8s LWIR bands are on the trailing edge of smoldering phase radiant emissions. After examining the LWIR fire features, we conclude that they are the result of smoldering phase combustion. This has been confirmed with field validation. Detection limits for smoldering peat fires in Landsat 8 is in the 40–90 m2 range. These results could lead to improved management of peatland fires and emission modeling.

Using the Short-Wave Infrared for Nocturnal Detection of Combustion Sources in VIIRS Data

Night-time images from the SNPP satellite VIIRS scanning radiometer in visible and infrared spectral bands provide invaluable data for detection and characterization of natural and technological combustion sources on the surface of the Earth, such as forest fires, gas flares, steel mills or active volcanoes. The presence of sub-pixel hot infrared (IR) emission sources can be readily detected at night in 1.6 micron near-infrared M10 channel. Their temperature and radiant heat intensity can be estimated by fitting of the Planck black-body spectral curve to the observed radiances of VIIRS infrared M-channels out to 4 um. VIIRS instrument is sensitive to the IR sources over a wide range of temperatures. This method can discriminate low temperature sources such as volcanoes and forest fires from the high temperature gas flares with 300 m average location error. The processing includes correction for panoramic “bow-tie” effect and filtering of the false detections resulting from sensor bombardment by the cosmic rays, especially at the aurora rings and at the South Atlantic anomaly. False detections can be largely removed by correlating of the observed bright spots in M10 channel with other infrared and the visible day-night band. NGDC NOAA provides global daily detection products for thousands of IR sources as KMZ vector maps and as CSV tables.

Daytime gas flare detection using Landsat-8 multispectral data

Daytime flaring detection using Landsat-8 multispectral data was inspired by the Visible Infrared Imaging Radiometer Suite (VIIRS) nightfire detection work. A fast and semi-automated endmember extraction algorithm was employed to detect gas flares in several locations of Alberta. Most of the detected flaring locations matched with the flaring reports, Bing Maps Aerial, and Google Maps images. To our knowledge, this is the only advanced technique for detecting daytime gas flares.

Rating the Effectiveness of Fishery Closures With Visible Infrared Imaging Radiometer Suite Boat Detection Data

Fishery closures are widely used to promote the sustainability of fish stocks. Fishery agencies typically have very little data relevant to planning closure enforcement actions and evaluating the effectiveness of closures, due in part to the vast expanse and remote nature of many closures. In some cases the effectiveness of closures can be evaluated using data from GPS based beacons, such as Automatic Identification System (AIS) or Vessel Monitoring Systems (VMS) installed on fishing boats. In fisheries where few boats are equipped with AIS or VMS, the rating of closures relies on other data sources capable of detecting or inferring fishing activity. One such source comes from low light imaging data collected by the NASA/NOAA Visible Infrared Imaging Radiometer Suite (VIIRS), which can detect fishing boats using lights to attract catch. This is a widely used practice in Asia and several other regions. NOAA has developed an automatic system for reporting the locations of VIIRS boat detections with a nominal four hour temporal latency. VIIRS boat detection alerts are running for more than 900 fishery closures in the Philippines, with email and SMS transmission modes. These alerts are being actively used in the Philippines to plan enforcement actions and there is a growing list of apprehensions that occurred based on tip-offs from VIIRS. The VIIRS boat detection archive extends back to April 2012. A VIIRS closure index (VCI) has been developed to rate the effectiveness of closures on monthly increments in terms of a percentage. The VCI analysis was performed on three types of closures: an ad hoc fishery closure associated with a toxic industrial discharge, a seasonal fishery closure and a permanent closure in restricted coastal waters. The VCI results indicate that it is possible to rank the effectiveness of different closure, year-to-year differences in compliance levels, and to identify closure encroachments which may warrant additional enforcement effort.

Estimating in-use steel stock of civil engineering and building in China by nighttime light image

China is dramatically changing due to rapid development in recent years. This can be observed from the change in landscapes, which most resulted from new or replaced constructions. The floor area of residential and commercial construction had increased fourfold from 1990 to 2005, and its speed does not show any sign of slowing down. The construction will also drive the demand of steel, which comprises half of the total national consumption. However, there were not many studies aiming to quantify the construction steel stock in China, which was mainly due to lack of statistical data. In order to overcome this obstacle, we proposed a methodology to estimate sub-national steel stock using nighttime light image. As a result, we found out that the Beijing municipality possesses the most construction steel stock. Most construction steel stock exists on the eastern coast, and is most concentrated in the Beijing municipality, the Tianjin municipality, the Shanghai municipality, and the Guangdong province.

Supporting international efforts for detecting illegal fishing and GAS flaring using viirs

The Visible Infrared Imaging Radiometer Suite (VIIRS) collects two styles of low light imaging data at night, enabling the detection of electric lighting and combustion sources. NOAA operates two near-real time processing chains to exploit the low light imaging data collected by VIIRS. One is focused on the detection of heavily lit fishing boats, providing fishery agencies with information related to illegal fishing. This paper provides an overview of the two products and reviews the uses that have been developed for the data.