Transitioning from MODIS to VIIRS: an analysis of inter-consistency of NDVI data sets for agricultural monitoring

ABSTRACT

The Visible/Infrared Imager/Radiometer Suite (VIIRS) aboard the Suomi National Polar-orbiting Partnership (S-NPP) satellite was launched in 2011, in part to provide continuity with the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument aboard National Aeronautics and Space Administration’s (NASA) Terra and Aqua remote-sensing satellites. The VIIRS will eventually replace Aqua MODIS for both land science and applications and add to the coarse-resolution, long-term data record. It is, therefore, important to provide the user community with an assessment of the consistency of equivalent products from the two sensors. For this study, we do this in the context of example agricultural monitoring applications. Surface reflectance that is routinely delivered within the M{O,Y}D09 and VNP09 series of products provides critical input for generating downstream products. Given the range of applications utilizing the normalized difference vegetation index (NDVI) generated from the M{O,Y}D09 and VNP09 products and the inherent differences between MODIS and VIIRS sensors in calibration, spatial sampling, and spectral bands, the main objective of this study is to quantify uncertainties associated with transitioning from using MODIS to VIIRS-based NDVIs. In particular, we compare NDVIs derived from two sets of Level 3 MYD09 and VNP09 products with various spatial-temporal characteristics, namely 8-day composites at 500 m spatial resolution and daily climate modelling grid images at 0.05° spatial resolution. Spectral adjustment of VIIRS I1 (red) and I2 (near infra-red – NIR) bands to match MODIS/Aqua b1 (red) and b2 (NIR) bands is performed to remove a bias between MODIS and VIIRS-based red, NIR, and NDVI estimates. Overall, red reflectance, NIR reflectance, and NDVI uncertainties were 0.014, 0.029, and 0.056, respectively, for the 500 m product and 0.013, 0.016, and 0.032 for the 0.05° product. The study shows that MODIS and VIIRS NDVI data can be used interchangeably for applications with an uncertainty of less than 0.02–0.05, depending on the scale of spatial aggregation, which is typically the uncertainty of the individual data sets.

Acknowledgement

This research was funded within the NASA Suomi NPP Science Team, Grant NNX14AR43A. The authors would like to acknowledge Dr Varaprasad Bandaru for raising a number of considerations in MODIS and VIIRS inter-use.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the National Aeronautics and Space Administration [NNX14AR43A];