Model Development for Nighttime Light Radiative Transfer and Application to VIIRS Day Night Band (DNB)

The observation of nighttime aerosol condition is important because of aerosol effects on visibility, air quality, and public health. By measuring visible light at night from space, the Visible Infrared Imaging Radiometer Suite Day/Night Band (VIIRS DNB) sensor onboard the NPP and JPSS-1 satellites provide the research and operational communities the capability to explore nighttime atmospheric optical and aerosol properties. To quantitatively use the data from DNB for nighttime remote sensing, we developed a nighttime radiative transfer model for DNB based on Unified Linearized Vector Radiative Transfer Model (UNL-VRTM; http://www.unl-vrtm.com). With the new development, UNL-VRTM can simulate light transfer at night with careful consideration of surface light spectra from various types of artificial light sources, gas flares, and wildfires, as well as moonlight and DNB Relative Sensor Response function (RSR).

We used this model to investigate questions key to the remote sensing of aerosol for VIIRS DNB observation: (1) How significant can VIIRS RSR impact the AOD retrieval if surface light spectra is wavelength independent (or uniform)? (2) How much AOD retrieval bias can it be under the assumption that the surface light spectra is nearly uniform for various (realistic) conditions with different kinds of lamp spectra? (3) if we only want to use one wavelength to simulate the radiance observed by DNB sensor at the spectral range of 400 - 900 nm, what is the most equivalent wavelength for different lamp spectra? Our preliminary results show that: (1) Without considering the DNB RSR, there can be 20% bias in AOD retrieval uncertainty, and the retrieval can be non-physical when AOD is low. (2) AOD retrieval bias is 10% if a uniform surface spectra is used in RTM with RSR considered. (3) 550 600 nm is the common DNB equivalent wavelength interval of our daily life lamps.