Introduction

There are several NASA satellite remote sensing aerosol products available for research and public use.  This users guide will focus on aerosol products created using the Dark Target (DT) algorithm(s) for MODIS and VIIRS.  A pdf of the User's Guide can be downloaded from this link.

The DT products have been in use since the launch of the polar orbiting Terra MODIS sensor in 1999 and on Aqua MODIS since 2002.  DT products have been adapted to the Visible Infrared Imaging Radiometer Suite (VIIRS) sensor. Two VIIRS instruments are currently in orbit, aboard Suomi-NPP and NOAA20 (JPSS-1), and future launches are planned. DT products are also in the process of being ported to the Advanced Baseline Imager (ABI) on the  geosynchronous orbiting GOES-R satellite series as well as the Advanced Himawari Imager (AHI) on the Himawari satellite platform.

Owing to the long association of the DT products with the MODIS sensor this guide has been written with a focus on the MODIS DT.   There are many similarities between the MODIS and VIIRS products so much of the information in the guide is also applicable to VIIRS. When differences occur each section of the guide will also include specific instructions for VIIRS.

This guide will focus on the DT products and their proper usage but will not go into detail on the DT algorithm.  A comprehensive description of the MODIS DT algorithm, the Algorithm Theoretical Basis Document (ATBD), is available in the ATBD section of NASA’s Dark Target website https://darktarget.gsfc.nasa.gov/.    As with this guide sections pertaining to the algorithm adjustments for VIIRS can also be found on the dark target website.

All satellite remote sensing aerosol products must contend with the problem of separating the aerosol signal from the surface signal observed by the sensor.  The DT algorithm relies on the phenomena that aerosols over a dark surface target will generally brighten the observed scene in order to separate these signals.

Where the surface is bright, such as over ocean glint or desert areas, the DT algorithm will not create a product retrieval. NASA also provides MODIS and VIIRS Deep Blue (DB) products which are more successful in providing aerosol information over bright surfaces. There is a combined MODIS DT-DB land product which attempts to merge the best retrievals from both products. The merged product will also be discussed in this guide.  DB will only be discussed in this guide in terms of its availability in the merged product. For more information on MODIS or VIIRS DB please visit their website.

There is also a higher resolution MODIS aerosol product the Multi-Angle Implementation of Atmospheric Correction product (MAIAC).  MAIAC will not be covered in this guide. For more information look here.