SPECIAL SECTION: HYPERSPECTRAL IMAGING CURRENT SCIENCE, VOL. 116, NO. 7, 10 APRIL 2019 1082 *For correspondence. (e-mail: bkbhattacharya@sac.isro.gov.in) An overview of AVIRIS-NG airborne hyperspectral science campaign over India Bimal K. Bhattacharya 1, *, Robert O. Green 2 , Sadasiva Rao 3 , M. Saxena 1 , Shweta Sharma 1 , K. Ajay Kumar 1 , P. Srinivasulu 3 , Shashikant Sharma 1 , D. Dhar 1 , S. Bandyopadhyay 4 , Shantanu Bhatwadekar 4 and Raj Kumar 1 1 Space Applications Centre, Indian Space Research Organisation, Ahmedabad 380 015, India 2 Jet Propulsion Laboratory, California Institute of Technology, CA 91109, USA 3 National Remote Sensing Centre, Indian Space Research Organisation, Hyderabad 500 625, India 4 Earth Observation Science Directorate, Indian Space Research Organisation, Bengaluru 560 231, India The first phase of an airborne science campaign has been carried out with the Airborne Visible/Infrared Imaging Spectrometer Next Generation (AVIRIS-NG) imaging spectrometer over 22,840 sq. km across 57 sites in India during 84 days from 16 December 2015 to 6 March 2016. This campaign was organized under the Indian Space Research Organisation (ISRO) and National Aeronautics and Space Administration (NASA) joint initiative for HYperSpectral Imaging (HYSI) programme. To support the campaign, synchronous field campaigns and ground measurements were also carried out over these sites spanning themes related to crop, soil, forest, geology, coastal, ocean, river water, snow, urban, etc. AVIRIS-NG measures the spectral range from 380 to 2510 nm at 5 nm sampling with a ground sampling distance ranging from 4 to 8 m and flight altitude of 4–8 km. On-board and ground-based calibration and processing were carried out to gener- ate level 0 (L0) and level 1 (L1) products respectively. An atmospheric correction scheme has been developed to convert the measured radiances to surface reflectance (level 2). These spectroscopic signatures are intended to discriminate surface types and retrieve physical and compositional parameters for the study of terre- strial, aquatic and atmospheric properties. The results from this campaign will support a range of objectives, including demonstration of advanced applications for societal benefits, validation of models/techniques, de- velopment of state-of-the-art spectral libraries, testing and refinement of automated tools for users, and defi- nition of requirements for future space-based missions that can provide this class of measurements routinely for a range of important applications. Keywords: Airborne science campaign, hyperspectral sensing, imaging spectrometer, surface reflectance. Introduction HYPERSPECTRAL sensing (HSS) of the land, water and atmosphere is based on the technique of imaging spec- troscopy, where a complete spectrum is measured for every point in an image. These spectra record the interac- tion of energy with matter and enable the use of advanced spectroscopic methods to determine the properties of the materials measured. Molecular and structural or particle characteristics of the surface or atmosphere produce diagnostic spectral features in the measurements. These features arise from electronic transition and vibrational processes as well as scattering effects, and are related to the fundamental material composition. Generally, elec- tron transition signatures occur at shorter wavelengths related to changes in energy state of electrons bound to atoms, molecules or lattices. Vibrational signatures typi- cally occur at longer wavelengths due to molecular bond stretching and bending along with related overtones. HSS refers to the measurement of 100s of contiguously sampled spectral channels with a relatively narrow sam- pling interval of 1–15 nm. In contrast, Multi-Spectral Sensing (MSS) typically corresponds to 5–10 discrete bands with bandwidths of 50–400 nm. Advantages of HSS are: (i) detection of more materials or surface types such as minerals, rocks, vegetation, snow; (ii) capture of full spectral signatures related directly to composition; (iii) recording the absorption strength that can be related to the abundance of the materials present, and (iv) the ability to derive sub-pixel abundance estimates for multiple materials recorded in a spectrum. HSS offers opportunities for new science and applications with broad societal benefits. The technology-enabling development of high-fidelity HSS instruments has only recently begun (Airborne Visible/Infrared Imaging Spec- trometer Next Generation (AVIRIS-NG) was developed in 2012). Laboratory and portable point spectrometers have been available for a longer period, but are severely limited in their sampling ability. Recently, several new HSS instruments such as micro-hyperspec and nano- hyperspec have become available providing centimetre spatial resolution from airborne, vehicle and mast- mounted platforms. Technology demonstration through HSS spaceborne missions, such as EO-1 Hyperion of National Aeronautics and Space Administration (NASA),