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Accurate Nightlight for Satellite Calibration for Weather and Climate Applications

Description:

Summary: The excellent on-orbit performance of the Suomi NPP VIIRS Day Night Band (DNB) ushers in a new era of low light imaging at night.  Its extreme sensitivity to low lights has already been demonstrated in numerous emerging applications, e.g., the rescue of a Bering Sea Fleet crab fishing vessel trapped in ice in the winter of 2013 in Alaska.  This unprecedented capability heavily depends on its onboard calibration, which unfortunately has one significant limitation:  it relies on solar signal which is more than seven orders of magnitudes brighter than the faint lights from fishing vessels.  As a result, the absolute calibration accuracy for the low night light is no better than 15%.  Also, the stability of the calibration for low light over time cannot yet be verified.  A significant calibration issue may diminish the ability in distinguishing fishing vessels from noise.  Furthermore, since the fishing light is typically a point source, both radiometric and spatial response of the DNB must be evaluated together, which is not possible with traditional methods.  This leads to the unmet needs for accurate (3× better) active light sources at night to validate and monitor the DNB responses to maintain its performance.  This will allow us to continue assisting in search and rescue of manmade faint light objects under severe weather conditions such as Hurricanes and Ice storms, helping the society to prepare for and respond to weather related events.  It will also allow us to monitor the light intensity of human settlements and their energy use, and many other natural low light phenomena over time, to study climate change and its anthropogenic contributions

 

Project Goals:  The goals of this project are to develop and deploy accurate active light sources (AALS) to selected calibration sites for the calibration/validation of the VIIRS DNB low light performance.  The long term stability of the AALS, after characterizing and correcting any systematic drift, should be maintained at 1%, and the absolute accuracy of the light sources should be better than 5%.  The AALS will only be turned on during the VIIRS DNB overpass at night around 1:30am local time.  The light intensity should be higher than 3×10-9 W/cm2·sr in order to be useful for DNB calibration.  These light sources will be used as benchmarks for comparisons with objects of interest on the DNB imagery.  Once the methodology is demonstrated at one site, it can be expanded to many other sites, potentially internationally.

 

Phase I Activities and Expected Deliverables:

·         Study the feasibility of using SI traceable active night light source for the calibration/validation of VIIRS DNB for low light conditions at the top of the atmosphere in clear sky conditions with radiances between 3×10-9 to 1×10-8 W/cm2·sr

·         Perform trade studies with different approaches, such as direct illumination versus reflected target; choices of light sources

·         Predict the long-term stability and absolute accuracy given the best and worst case scenarios

·         Analyze the error budgets both at the light source and top of the atmosphere

·         Evaluate alternative methodologies that may complement the active light source

·         Develop concept of operations for accurate active light sources that can be deployed to selected sites to be detected by VIIRS DNB within ±10 degree scan angles; the absolute accuracy of the light source in radiances should be better than 5% in clear sky conditions

 

Phase II Activities and Expected Deliverables:

·         Design and develop prototype units and calibrate them in the laboratory

·         Deploy the unit to selected site for demonstration

·         Demonstrate the viability of long term operations of the AALS for selected sites

·         Select at least 3 sites for the AALS deployment and study the site suitability and variations in error budgets

·         Study the stability of the light source at each site (expected to be better than 1% per year)

·         Deploy the AALS to the 3 sites and demonstrate their operations

·         Conduct market research on the commercialization of the AALS

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