Exploring the Potential of DSCOVR EPIC Data to Retrieve Clumping Index in Australian Terrestrial Ecosystem Research Network Observing Sites

Jan Pisek,Angela Erb,William Woodgate,Elise Pendall,Crystal Schaaf,Stefan K Arndt,Yuri Knyazikhin,Timothy J Wardlaw

doi:10.3389/frsen.2021.652436

Abstract

Vegetation foliage clumping significantly alters the radiation environment and affects vegetation growth as well as water, carbon cycles. The clumping index (CI) is useful in ecological and meteorological models because it provides new structural information in addition to the effective leaf area index. Previously generated CI maps using a diverse set of Earth Observation multi-angle datasets across a wide range of scales have all relied on the single approach of using the normalized difference hotspot and darkspot (NDHD) method. We explore an alternative approach to estimate CI from space using the unique observing configuration of the Deep Space Climate Observatory Earth Polychromatic Imaging Camera (DSCOVR EPIC) and associated products at 10 km resolution. The performance was evaluated with in situ measurements in five sites of the Australian Terrestrial Ecosystem Research Network comprising a diverse range of canopy structure from short and sparse to dense and tall forest. The DSCOVR EPIC data can provide meaningful CI retrievals at the given spatial resolution. Independent but comparable CI retrievals obtained with a completely different sensor and new approach were encouraging for the general validity and compatibility of the foliage clumping information retrievals from space. We also assessed the spatial representativeness of the five TERN sites with respect to a particular point in time (field campaigns) for satellite retrieval validation. Our results improve our understanding of product uncertainty both in terms of the representativeness of the field data collected over the TERN sites and its relationship to Earth Observation data at different spatial resolutions.

Highlights

The clumping index (CI) quantifies the level of foliage grouping within distinct canopy structures relative to a random distribution (Nilson, 1971; Chen and Black, 1992)
The landscape heterogeneity within the Deep Space Climate Observatory (DSCOVR) Earth Polychromatic Imaging Camera (EPIC) Vegetation Earth System Data Record (VESDR) product pixel resolution manifested itself in the agreement with the in situ measured values of CI over the different sites
Good agreement between the EPIC CI-derived value and in situ measurements (i.e., EPIC CI retrievals intersecting with the vertical profiles collected with digital hemispherical photography (DHP)) was observed over the most homogeneous sites, Tumbarumba (Figure 2B) and Warra (Figure 2E)

Summary

Introduction

The clumping index (CI) quantifies the level of foliage grouping within distinct canopy structures relative to a random distribution (Nilson, 1971; Chen and Black, 1992). It provides best agreement between transmittance through clumped canopy and Beer’s exponential transmission law (Nilson, 1971; Kuusk, 2018). The distribution of foliar nutrients and canopy evapotranspiration (ET) were found to be significantly influenced by CI (Thomas et al, 2011) Both ground and satellite ET estimates are greatly underestimated if CI is not considered (Chen et al, 2016). CI is an important parameter for accurate canopy-level gross primary production (GPP) modeling (Ryu et al, 2011; Chen et al, 2012)

Methods

Results

Conclusion