Vegetation hot spot signatures from synergy of DSCOVR EPIC, Terra MISR, MODIS and geostationary sensors

It has been widely recognized that the hotspot region in Bidirectional Reflectance Factors (BRF) of vegetated surfaces represents the most information-rich directions in the directional distribution of canopy reflected radiation. The hotspot effect is strongly correlated with canopy architectural parameters such as foliage size and shape, crown geometry and within-crown foliage arrangement, leaf area index and its sunlit fraction. Here we present a new methodology that synergistically incorporate features of Terra Multi-angle Imaging SpectroRadiometer (MISR) and Moderate Resolution Imaging Spectroradiometer (MODIS), Aqua MODIS, Earth Polychromatic Imaging Camera (EPIC) onboard the Deep Space Climate Observatory (DSCOVR), Advanced Baseline Imager (ABI) carried by the Geostationary Operational Environmental Satellites (GOES) R series and Advanced Himawari Imager (AHI) observation geometries and results in a new type of hot spot signatures that maximally sensitive to vegetation changes. We discuss a physical basis for the synergy of multi-sensor data. Five areas that include Amazonian forests (evergreen broadleaf forest), Mississippi forest (deciduous forest), Heihe River Basin (crops), Genhe forest (coniferous forest) and Australia central grassland were selected to generate time series of hot spot signatures of different land cover types for the period of concurrent Terra/Aqua/DSCOVR and geostationary observations. We demonstrate value of the hot spot signatures for monitoring changes and biophysical processes in vegetated land through analyses of variations in magnitude and shape of angular distribution of canopy reflected radiation and the rigorous use of radiative transfer theory.Accepted manuscrip

DSCOVR EPIC vegetation earth system data record: product analysis and scientific exploration

The NASA's Earth Polychromatic Imaging Camera (EPIC) onboard NOAA's Deep Space Climate Observatory (DSCOVR) mission was launched on February 11, 2015 to the Sun-Earth Lagrangian L1 point where it began to collect radiance data of the entire sunlit Earth every 65 to 110 min in June 2015. It provides imageries in near backscattering directions at ten ultraviolet to near infrared narrow spectral bands. The DSCOVR EPIC science product suite includes vegetation Earth System Data Record (VESDR) that provides leaf area index (LAI) and diurnal courses of normalized difference vegetation index (NDVI), sunlit LAI (SLAI), fraction of incident photosynthetically active radiation (FPAR) and directional area scattering function (DASF). The parameters at 10 km sinusoidal grid and 65 to 110 minute temporal frequency generated from the upstream DSCOVR EPIC BRF product were released on June-07-2018 and are available from the NASA Langley Atmospheric Science Data Center. This poster provides an overview of the EPIC VESDR research. This includes a description of the algorithm and its performance, details of the product, its initial quality assessment and obtaining new information on the 3D canopy structure for use in ecological models through novel combinations of the VESDR parameters.Accepted manuscrip

Vegetation hot spot signatures from synergy of EPIC/DSCOVR, MISR/Terra, MODIS and geostationary sensors to monitor changes and biophysical processes of global forests

Accepted manuscrip

High efficiency near diffraction-limited mid-infrared flat lenses based on metasurface reflectarrays

A limiting factor in the development of mid-infrared optics is the lack of abundant materials that are transparent, low cost, lightweight, and easy to machine. In this paper, we demonstrate a metasurface device that circumvents these limitations. A flat lens based on antenna reflectarrays was designed to achieve near diffraction-limited focusing with a high efficiency (experiment: 80%, simulation: 83%) at 45(o) incidence angle at {\lambda} = 4.6 {\mu}m. This geometry considerably simplifies the experimental arrangement compared to the common geometry of normal incidence which requires beam splitters. Simulations show that the effect of comatic aberrations is small compared to parabolic mirrors. The use of single-step photolithography allows large scale fabrication.Comment: 9 page

Angular signatures of vegetated land

First author draf

DSCOVR EPIC Vegetation Earth System Data Record (DSCOVR EPIC L2 VESDR),

Accepted manuscrip

Vegetation hot spot signatures from synergy of EPIC/DSCOVR and EOS/SUOMI sensors to monitor changes in global forests

Published versio

Seasonal variation of Congo rainforests from DSCOVR/EPIC and MISR observations

Knowledge of seasonal variation of tropical rainforests are essential for understanding its response to the climate change. The equatorial Congo rainforest, the second-largest on Earth, however is still lacking of systematic analyses of seasonal variation in forest greenness with strong observational evidences. This poster investigates the seasonality of the Congo rainforest with Deep Space Climate Observatory (DSCOVR) Earth Polychromatic Imaging Camera (EPIC) and Multi-angle Imaging SpectroRadiometer (MISR) datasets. The monthly mean near-infrared (NIR) bidirectional reflectance factor (BRF) from EPIC of 2016-2019 exhibits a bimodal pattern over the Congo forest, which is consistent with the seasonality of leaf area from MODIS LAI (Collection 6) and precipitation from TRMM. Analyses of NIR BRF angular signatures from MISR and EPIC further confirms that more green leaves appear during the wet season compared to the dry season. Variation in the canopy scattering coefficient (CSC) suggests a higher leaf absorption in wet season than in dry season, which is attributed to a higher concentration of chlorophyll and/or dry matter in leaves. This research also demonstrates the complementarity and consistency between DSCOVR/EPIC records and existing data from polar-orbiting satellites in tropical rainforest monitoring, and the CSC will be provided in the upcoming version of DSCOVR/EPIC Vegetation Earth System Data Record (VESDR) science product.Published versio

High efficiency near diffraction-limited mid-infrared flat lenses based on metasurface reflectarrays

We report the first demonstration of a mid-IR reflection-based flat lens with high efficiency and near diffraction-limited focusing. Focusing efficiency as high as 80%, in good agreement with simulations (83%), has been achieved at 45° incidence angle at λ = 4.6 μm. The off-axis geometry considerably simplifies the optical arrangement compared to the common geometry of normal incidence in reflection mode which requires beam splitters. Simulations show that the effects of incidence angle are small compared to parabolic mirrors with the same NA. The use of single-step photolithography allows large scale fabrication. Such a device is important in the development of compact telescopes, microscopes, and spectroscopic designs