Retrieval of 500 m Aerosol Optical Depths from MODIS Measurements over Urban Surfaces under Heavy Aerosol Loading Conditions in Winter

Shikuan Jin,Yingying Ma,Yifan Shi,Oleg Dubovik,Ming Zhang,Wei Gong,Changlan Yang,Boming Liu

doi:10.3390/rs11192218

Abstract

Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol products are used worldwide for their reliable accuracy. However, the aerosol optical depth (AOD) usually retrieved by the operational dark target (DT) algorithm of MODIS has been missing for most of the urban regions in Central China. This was due to a high surface reflectance and heavy aerosol loading, especially in winter, when a high cloud cover fraction and the frequent occurrence of haze events reduce the number of effective satellite observations. The retrieval of the AOD from limited satellite data is much needed and important for further aerosol investigations. In this paper, we propose an improved AOD retrieval method for 500 m MODIS data, which is based on an extended surface reflectance estimation scheme and dynamic aerosol models derived from ground-based sun-photometric observations. This improved method was applied to retrieve AOD during heavy aerosol loading and effectively complements the scarcity of AOD in correspondence with urban surface of a higher spatial resolution. The validation results showed that the retrieved AOD was consistent with MODIS DT AOD (R = ~0.87; RMSE = ~0.11) and ground measurements (R = ~0.89; RMSE = ~0.15) from both the Terra and the Aqua satellite. The method can be easily applied to different urban environments affected by air pollution and contributes to the research on aerosol.

Highlights

Aerosols consist of particles with different chemical compositions, optical properties, shape, and size, which have significant impacts on the global climate changes [1]
The Moderate Resolution Imaging Spectroradiometer (MODIS) operational land Dark Target (DT) aerosol retrieval algorithm is based on two main assumptions [16]: (1) the existence of a linear relationship between the short-wave infrared reflectance of the surface (2.12 μm) and the visible bands corresponding to the dense dark vegetation pixels; (2) the mixing of several predefined aerosol types
In order to assess our aerosol optical depth (AOD) retrieval method which is proposed here, both MODIS sensors images were processed over Wuhan from the last three winters

Summary

Introduction

Aerosols consist of particles with different chemical compositions, optical properties, shape, and size, which have significant impacts on the global climate changes [1]. A large amount of water vapor is released by rivers and lakes (Figure 1) located around the city, resulting in high humidity all year around These conditions lead to the hygroscopic growth of the aerosol particles, influencing the gas-particle conversion rates, and the formation of local haze [22,23,24]. 5(3].)TDhuerAinAgMexsthreomwes air polhluigtihonapbesroiropdtsi,otnhecnoummpbaererdanwd istihzeDofevneolno-paibnsgorbainndg fiUnrebmano-dInedpamrtoicdleslscointinthuee tMo OinDcrIeSasDe.TIt is proablagbolryithdmue wtohtihceh inarcereagseeneorfatlhlye ruastedofingaCs-hpianrat.icTlehceondvyenrasmioinc aanedropsaorltimcloedheylsgrdosecsocrpiibcegtrhoewth undcheranhgigehs ohfuameridositoyl cmoonrdeitaicocnusr.aBtealsyedanodnatrheebaebnoevfieciuanl dinersettarniedviinngg, AwOeDclafrsosimfiepdaasseirvoesosalst’eollpitteical proipmeargtiess,, eusspinecgiamlleyaisnurheemaveyntaseorof stohlelCoaEd-i3n1g8 cfroonmdit2i0o1n2s tion 2w0h1i6c,hemthpelaoeyrionsgolasKig-nmaelaoncscuclpuisetsearing applarorgaecrh ptoroopbotratiinontwoof AthOeDtodteapl esnigdneanlc.eAaletrhoosuogl hmothdeelcsla[3s3si]c: aal rceolantivnenstcaalttaeerirnogsoalemroosodlelmiosdel (SAsMug)gaensdteadnnaobtstoorbiencgoanedruocsoivlemtodreltr(iAevAaMl a)e, raosssohlsowbencainusFeigouf riets2i.nTdheepetwndoeanecreofsroolmmAodOeDls,witere relaitsivsteillyl uinsdeefuplentodednetscarnidbethneaitnuprault ccohnatriancetenrtiasltibcapcakrgarmouetnedrsaienrcolsuosltse.rIannaadlydsiitsiowne,rtehseiningcleresacsaetteinring albeaderoo(sSoSlAp)aartti6c7le0 nsimzeanddueastyomhmygetrroyscfaocptiocr gatro4w40thnmistuonadvoeridesctrimeaatitnegd ainduMstOcDluIsSteDr fTroamlguolrtirtahvmiolet absaoerrpotsionl m(aotdneelasru4n4d0enrmhi)g[h33h,3u4m].idity conditions such as in Central and Southern China Those inappropriate assumptions of aerosols may result in inaccurate and failed AOD retrievals. The refractive index shows the absorbing and scattering characteristics of aerosol particles at 670 nm

Surface Reflectance

Retrieval Strategy

Retrieval Results