MODIS BRDF effects over Brazilian tropical forests and savannahs: a comparative analysis

Petri, Caio Arlanche; Galvão, Lênio Soares; Lyapustin, A.

doi:10.1080/2150704x.2018.1526425

Cited by 5 publications

(4 citation statements)

References 9 publications

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“…In relation to the VZA, the retrievals of high-quality pixels increase gradually from north to south of the Amazon and toward the beginning of the dry season. These retrievals reach a maximum in the middle of the dry season in the southern Amazon (July to August) [5,9]. In the northern Amazon (site 1), the persistent cloud cover decreases the frequency of high-quality pixels.…”

Section: Discussionmentioning

confidence: 98%

“…Thus, depending on the VI used in the analysis, the effects of the bidirectional reflectance distribution function (BRDF) can add a significant non-biophysical signal into the time series [8]. In Amazonian tropical forests, BRDF effects are still present even in MODIS VI composite products because of the adverse conditions of the atmosphere to allow retrievals of nadir observations [9].…”

Section: Introductionmentioning

confidence: 99%

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Sensitivity of Seven MODIS Vegetation Indices to BRDF Effects during the Amazonian Dry Season

Petri

Galvão

2019

Remote Sensing

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We used Moderate Resolution Imaging Spectroradiometer (MODIS) data, processed by the multi–angle implementation of atmospheric correction (MAIAC) algorithm, to investigate the sensitivity of seven vegetation indices (VIs) to bidirectional reflectance distribution function (BRDF) effects in the dry season (June–September) of the Brazilian Amazon. The analysis was first performed over three sites, located from north to south of the Amazon, and then extended into the entire region. We inspected for differences in viewing–illumination parameters and pixel quality retrievals during MODIS data acquisition over the region. By comparing and correlating corrected and non–corrected data for bidirectional effects, we evaluated monthly changes in reflectance and VIs (2000–2014). Finally, we computed the effect size of the BRDF correction using non–parametric Mann–Whitney tests and Cohen’s r metrics. The results showed that the most anisotropic VIs were the enhanced vegetation index (EVI), photochemical reflectance index (PRI), and shortwave infrared normalized difference (SWND). These VIs presented the largest relative changes and the lowest correlation coefficients, between corrected and non–corrected data, because of the large effect size of the BRDF. The least anisotropic VI was the normalized difference water index (NDWI). The anisotropy of these VIs was stronger in the northern Amazon. It increased from the beginning to the end of the dry season, following changes in the relative azimuth angle (RAA) toward the BRDF hotspot in September. The modifications in the relative proportions of backscattering observations used in composite products caused a reflectance increase in all MODIS bands at the end of the dry season, especially in the near infrared (NIR). The reflectance decreased after BRDF correction. Because of the atmospheric effects, the view zenith angle (VZA) of the pixels selected in composite products decreased toward the south of the Amazon. In the southern Amazon, the seasonal amplitude in the solar zenith angle (SZA) reached values close to 18°. For the most anisotropic index, the BRDF correction removed, on average, 30% of the EVI signal in June, and 60% of the EVI signal in September, reducing dry season variations over time. The results reinforce the need for bidirectional correction of MODIS data before the seasonal and inter–annual analyses of the most anisotropic VIs.

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Section: Discussionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

Sensitivity of Seven MODIS Vegetation Indices to BRDF Effects during the Amazonian Dry Season

Petri

Galvão

2019

Remote Sensing

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“…It is worth mentioning that an angular normalization procedure is mandatory to reduce the confounding non-biophysical signals and to sustain the interpretation of the airborne imagery in respect to land surface properties. VHR airborne hyperspectral images acquired over a rugged topography requires disentanglement of soil, vegetation canopy, and relief BRDFs, which remains challenging [21][22][23]. The problem is even more complex with airborne data due to the strong influence of the local slope and aspect.…”

Section: Introductionmentioning

confidence: 99%

A Kernel-Driven BRDF Approach to Correct Airborne Hyperspectral Imagery over Forested Areas with Rugged Topography

et al. 2020

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Airborne hyper-spectral imaging has been proven to be an efficient means to provide new insights for the retrieval of biophysical variables. However, quantitative estimates of unbiased information derived from airborne hyperspectral measurements primarily require a correction of the anisotropic scattering properties of the land surface depicted by the bidirectional reflectance distribution function (BRDF). Hitherto, angular BRDF correction methods rarely combined viewing-illumination geometry and topographic information to achieve a comprehensive understanding and quantification of the BRDF effects. This is in particular the case for forested areas, frequently underlaid by rugged topography. This paper describes a method to correct the BRDF effects of airborne hyperspectral imagery over forested areas overlying rugged topography, referred in the reminder of the paper as rugged topography-BRDF (RT-BRDF) correction. The local viewing and illumination geometry are calculated for each pixel based on the characteristics of the airborne scanner and the local topography, and these two variables are used to adapt the Ross-Thick-Maignan and Li-Transit-Reciprocal kernels in the case of rugged topography. The new BRDF model is fitted to the anisotropy of multi-line airborne hyperspectral data. The number of pixels is set at 35,000 in this study, based on a stratified random sampling method to ensure a comprehensive coverage of the viewing and illumination angles and to minimize the fitting error of the BRDF model for all bands. Based on multi-line airborne hyperspectral data acquired with the Chinese Academy of Forestry’s LiDAR, CCD, and Hyperspectral system (CAF-LiCHy) in the Pu’er region (China), the results applying the RT-BRDF correction are compared with results from current empirical (C, and sun-canopy-sensor (SCS) adds C (SCS+C)) and semi-physical (SCS) topographic correction methods. Both quantitative assessment and visual inspection indicate that RT-BRDF, C, and SCS+C correction methods all reduce the topographic effects. However, the RT-BRDF method appears more efficient in reducing the variability in reflectance of overlapping areas in multiple flight-lines, with the advantage of reducing the BRDF effects caused by the combination of wide field of view (FOV) airborne scanner, rugged topography, and varying solar illumination angle over long flight time. Specifically, the average decrease in coefficient of variation (CV) is 3% and 3.5% for coniferous forest and broadleaved forest, respectively. This improvement is particularly marked in the near infrared (NIR) region (i.e., >750 nm). This finding opens new possible applications of airborne hyperspectral surveys over large areas.

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“…An important feature of Figure 5 is the bi-modal distribution of surface reflectance in all three bands in the 1st and 4th quarters. It relates to the fact that over tropics the MODIS scan geometry aligns with the principal plane in March and October providing observations close to the "dark spot" and to the "hot spot" of BRDF physically representing maximal and minimal shadowing, whereas in other months it moves away ∼20-60 °from the principal plane (Bi et al, 2015;Petri et al, 2019). Because the tile H11V09 is mostly homogeneous, the effect of clustering of SR at extreme values manifests the reflectance anisotropy (BRDF).…”

Section: Analysis Of High Quality Pixelsmentioning

confidence: 98%

A Comparison of Multi-Angle Implementation of Atmospheric Correction and MOD09 Daily Surface Reflectance Products From MODIS

Lyapustin

Zhao

Wang

2021

Front. Remote Sens.

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This study presents the first systematic comparison of MAIAC Collection 6 MCD19A1 daily surface reflectance (SR) product with standard MODIS SR (MOD/MYD09). The study was limited to four tiles located in mid-Atlantic United States (H11V05), Canada (H12V03), central Amazon (H11V09), and North-Eastern China (H27V05) and used over 5000 MODIS granules in 2018. Overall, there is a remarkable agreement between the best quality pixels of the two products, in particular in the Red and NIR bands. Over selected tiles, the evaluation found that MAIAC provides from 4 to 25% more high-quality retrievals than MOD09 annually, with the largest difference in tropical regions, confirming results of the previous studies. The comparison of spectral characteristics showed a systematic MAIAC-MOD09 difference increasing from NIR to Blue, typical of biases of a Lambertian assumption in MOD09 algorithm. Over the North-Eastern China, MCD19A1 SR is found more stable at wide range of aerosol optical depth (AOD) variations, whereas MOD09 SR shows a consistent positive bias increasing with AOD and at shorter wavelengths. The observed SR differences can be attributed to differences in cloud detection, aerosol retrieval and in atmospheric correction which is performed using an accurate BRDF-coupled radiative transfer model in MAIAC and a Lambertian surface model in MOD09. While this study is not representative of the global performance because of its limited geographical coverage, it should help the land community to better understand the differences between the two products.

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MODIS BRDF effects over Brazilian tropical forests and savannahs: a comparative analysis

Cited by 5 publications

References 9 publications

Sensitivity of Seven MODIS Vegetation Indices to BRDF Effects during the Amazonian Dry Season

Sensitivity of Seven MODIS Vegetation Indices to BRDF Effects during the Amazonian Dry Season

A Kernel-Driven BRDF Approach to Correct Airborne Hyperspectral Imagery over Forested Areas with Rugged Topography

A Comparison of Multi-Angle Implementation of Atmospheric Correction and MOD09 Daily Surface Reflectance Products From MODIS

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