Spatial-Temporal resolution implementation of cloud-aerosols data through satellite cross-correlation

Our knowledge of the temporal-spatial variations of atmospheric aerosols is necessary because they can affect public health and air quality. This paper studied Collection 6, the product of Aerosol Optical Depth (AOD 550 nm), using the Deep Blue algorithm of moderate-resolution imaging spectroradiometer (MODIS) on board the Terra and Aqua satellites over Iran from 2003 to 2017. Long-term data of the dust using synoptic stations were also used. The results showed that the southwestern Iran, the Persian Gulf coast from Bushehr to Bandar Abbas, and the Makran coastal area in southeastern Iran have the highest seasonal means of Aerosol optical depth (AOD > 0.3) and that they are among the aerosol hotspot areas in southwestern Asia. Other regions in Iran, especially the northwest and the Zagros Mountains, have the lowest aerosol optical depth (AOD < 0.04). The highest AOD amount of Terra (0.144) and Aqua (0.156) occurs in the spring, and the lowest amount occurs in the autumn season (0.094 and 0.101 Terra and Aqua, respectively). The heights act as a barrier on the particle transport pathway and, as a result, will affect the release of dust on local and regional scales. AOD increase in Iran is more related to aerosol loading in deserts and arid areas around the country. The AOD increase during the cold period of the year in industrial cities is due to the combustion of fossil fuels and the reduction of the boundary layer height (BLH). It is because most atmospheric pollutants are released in the boundary layer and are homogenized through turbulent mixed layer processes. The most prominent active dust sources around Iran, which are the main source of aerosol increase, can be categorized into four sources: (1) Mesopotamian, (2) Northern Arabian Peninsula, (3) Elrob Elkhali desert, and (4) East Arabian Peninsula. The AOD seasonal trend showed that the most significant increasing trend occurs in autumn on the TERRA (42.82%) and Aqua (32.32%) satellites. The largest decreasing trend of AOD in Iran is observed in winter in Kermanshah province (− 0.0011 year−1) in western Iran and in other seasons in southeastern Iran for which meteorological changes play a major role.

Objetivos: Determinar el espesor optico de los aerosoles (EOA) durante los meses de enero 2007 y 2008 y febrero de 2013 en la Estacion Cientifica Antartica Machu Picchu (ECAMP). Metodos: La investigacion fue descriptiva comparativa. Se utilizo el fotometro solar SP02-L para mediciones directas del sol con 4 sensores centrados en las longitudes de onda 412, 500, 675 y 862 nm. Se utilizo registros con un angulo cenital solar inferior a 80° y con cero de cobertura nubosa 30° alrededor del Sol. Estas mediciones fueron comparadas, a traves de la prueba de Pearson, con EOA a 550 nm de los sensores satelitales MODIS (Moderate Resolution Imaging Spectroradiometer). Resultados: Se determino una maxima y minima media de EOA de 0,1061 y 0,0616, respectivamente. Reporto un coeficiente de correlacion con el sensor MODIS, tanto del satelite Aqua y Terra, siendo 0,0284 y 0,0059 (p<0,05), respectivamente. La misma correlacion fue evaluada con el Indice de Aerosol del sensor OMI (Ozone Monitoring Instrument) resultando una mayor correlacion, 0,3606 (p<0,05). Comparando el EOA resultante en la ECAMP con las demas estaciones antarticas se encontraron valores similares alrededor de 0,06, en las zonas costeras como Neumayer y Aboa. Conclusiones: Los datos obtenidos en la ECAMP en los anos 2007, 2008 y 2013 no evidencian una variacion significativa respecto al espesor optico de aerosoles. Los altos valores obtenidos en la ECAMP comparados con las estaciones de Aboa y Neumayer pueden tener su explicacion en las mediciones manuales realizadas en comparacion con las automaticas de las otras estaciones.

Observations of the aerosol optical thickness (AOT) by the Moderate Resolution Imaging Spectroradiometer (MODIS) instruments aboard Terra and Aqua satellites are being used extensively for applications to climate and air quality studies. Data quality is essential for these studies. Here we investigate the effects of unresolved clouds on the MODIS measurements of the AOT. The main cloud effect is from residual cirrus that increases the AOT by 0.015/spl plusmn/0.003 at 0.55 /spl mu/m. In addition, lower level clouds can add contamination. We examine the effect of lower clouds using the difference between simultaneously measured MODIS and AERONET AOT. The difference is positively correlated with the cloud fraction. However, interpretation of this difference is sensitive to the definition of cloud contamination versus aerosol growth. If we consider this consistent difference between MODIS and AERONET to be entirely due to cloud contamination we get a total cloud contamination of 0.025/spl plusmn/0.005, though a more likely estimate is closer to 0.020 after accounting for aerosol growth. This reduces the difference between MODIS-observed global aerosol optical thickness over the oceans and model simulations by half, from 0.04 to 0.02. However it is insignificant for studies of aerosol cloud interaction. We also examined how representative are the MODIS data of the diurnal average aerosol. Comparison to monthly averaged sunphotometer data confirms that either the Terra or Aqua estimate of global AOT is a valid representation of the daily average. Though in the vicinity of aerosol sources such as fires, we do not expect this to be true.

Inter-comparison of integrated water vapor from satellite instruments using reference GPS data at the Iberian Peninsula

The Moderate Resolution Imaging Spectroradiometer (MODIS) aboard both NASA’s Terra and Aqua satellites is making near-global daily observations of the earth in a wide spectral range (0.41–15 μm). These measurements are used to derive spectral aerosol optical thickness and aerosol size parameters over both land and ocean. The aerosol products available over land include aerosol optical thickness at three visible wavelengths, a measure of the fraction of aerosol optical thickness attributed to the fine mode, and several derived parameters including reflected spectral solar flux at the top of the atmosphere. Over the ocean, the aerosol optical thickness is provided in seven wavelengths from 0.47 to 2.13 μm. In addition, quantitative aerosol size information includes effective radius of the aerosol and quantitative fraction of optical thickness attributed to the fine mode. Spectral irradiance contributed by the aerosol, mass concentration, and number of cloud condensation nuclei round out the list of available aerosol products over the ocean. The spectral optical thickness and effective radius of the aerosol over the ocean are validated by comparison with two years of Aerosol Robotic Network (AERONET) data gleaned from 132 AERONET stations. Eight thousand MODIS aerosol retrievals collocated with AERONET measurements confirm that one standard deviation of MODIS optical thickness retrievals fall within the predicted uncertainty of Δτ = ±0.03 ±0.05τ over ocean and Δτ = ±0.05 ± 0.15τ over land. Two hundred and seventy-one MODIS aerosol retrievals collocated with AERONET inversions at island and coastal sites suggest that one standard deviation of MODIS effective radius retrievals falls within Δreff = ±0.11 μm. The accuracy of the MODIS retrievals suggests that the product can be used to help narrow the uncertainties associated with aerosol radiative forcing of global climate.

Intra-annual variations of regional total column ozone, aerosol optical depth, and water vapor from ground-based, satellite-based and model-based observations

Climatological trends in satellite-derived aerosol optical depth over North India and its relationship with crop residue burning: Rural-urban contrast

The Moderate Resolution Imaging Spectroradiometer (MODIS), a key instrument of the NASA Earth Observing System missions, has operated for over 20 years and 18 years onboard the Terra and Aqua satellites, respectively. Sixteen thermal emissive bands (TEBs) are distributed on two cold focal place assemblies with photovoltaic (PV) HgCdTe detectors for bands 20-25 and 27-30 and photoconductive (PC) HgCdTe detectors for bands 31-36. This paper evaluates the performance of the latest MODIS Collection 6.1 (C6.1) Level-1B products with a focus on the relative differences between the Terra and Aqua MODIS TEBs. The Infrared Atmospheric Sounding Interferometer (IASI) onboard the Metop-A satellite serves as a reference. Observations obtained from the simultaneous nadir overpass between the Terra (or Aqua) and Metop-A satellites are used to track the brightness temperature differences between MODIS and IASI. The assessment is based on the temperature differences as a function of scene temperature and their trends in comparison with IASI from years 2007 to 2020. The results confirm that the calibration of Terra MODIS bands 27-30 significantly improved in C6.1 after implementing the electronic crosstalk correction. In spite of these corrections, Terra MODIS shows a larger drift in PV LWIR bands 27-30 than Aqua MODIS when compared to IASI.A sensitivity study is performed, where the center wavelength of the MODIS relative spectral response is shifted, and as a result some of these bands show a significant improvement in scene temperature dependency and their consistency with IASI measurements.

The Moderate Resolution Imaging Spectroradiometer (MODIS) is an Earth-observing sensor currently operational on the Earth Observing System (EOS) Terra and Aqua satellites. Each MODIS instrument has 36 spectral bands, with data acquired using 490 detectors in the reflective solar and thermal emissive spectrum. The 20 reflective solar bands (RSB), covering a wavelength range from 0.4 to 2.2 μm, are calibrated on-orbit using a solar diffuser (SD), solar diffuser stability monitor (SDSM) and regularly scheduled lunar measurements. The instrument gain (1/m1) derived from SD measurements and the response versus scan-angle (RVS) derived using the SD and lunar measurements are the primary look-up-tables (LUT) that are updated on a regular basis. The short wavelength bands of both MODIS instruments have experienced a gain change of up to 50% as observed from the SD calibration. Given the longevity of both MODIS sensors, the detectors have aged, and the sensor’s radiometric characteristics have changed since launch. A strong dependence of the RVS on mirror side, detector, wavelength and time is also observed in visible (VIS) channels. The MODIS Characterization Support Team (MCST) is responsible for deriving and updating the on-orbit calibration coefficients. An accurate and timely update of the LUT is vital for maintaining the quality of the calibrated Level 1B (L1B) product. This paper provides an overview of the MODIS RSB calibration along with the major procedures used to regularly update the LUT. In addition, the various lessons learned and future improvements are also discussed.

Evaluation of the surface PM2.5 in Version 1 of the NASA MERRA Aerosol Reanalysis over the United States

This work deals with the validation of integrated water vapor (IWV) products derived from the following satellite instruments: Global Ozone Monitoring Instrument (GOME-2), Moderate-Resolution Imaging Spectroradiometer (MODIS) on the Terra and Aqua satellites, Ozone Monitoring Instrument (OMI), Spining Enhanced Visible and InfraRed Imager (SEVIRI), Atmospheric Infrared Sounder (AIRS), and Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY). IWV data from GPS in nine ground-based stations located in the Iberian Peninsula are used as reference. The study period extends from 2007 to 2012, under cloud-free conditions. All satellite instruments showed a tendency to reduce IWV extreme values: low IWV is overestimated while high IWV is underestimated. As for the influence of solar zenith angle (SZA), Seasonal dependence is mainly due to the SZA and IWV typical values in each season. In general, in summer the tendency is to underestimate with low inter-quartile range (IQR) and in winter the trend is to overestimate with high IQR.

Techniques are presented for generating thermal infrared and visible composite images from cloud-free portions of MODIS (MODerate resolution Imaging Spectroradiometer) images closely spaced in time, with a focus on studies of landfast sea ice along the East Antarctic coast. Composite image inclusion criteria are based on modified MODIS EOS cloud mask product results. The compositing process places emphasis on retaining maximum spatial resolution while minimizing computing storage space requirements. Composite images can be produced either as a regular product (e.g., on a 10-day grid), or dynamically (whenever enough information is acquired to produce a new output image). The techniques presented are applicable at any latitude, are available for all MODIS channels at their native resolution, can combine Aqua and Terra images, and can produce maps in any output projection. However, due to the polar orbit of NASA's Terra and Aqua satellites which host the MODIS instrument, more frequent coverage is produced at higher latitudes. Thus, the techniques presented are particularly applicable to polar research. Examples of summertime (visible) and wintertime (IR) composite image generation of the landfast sea ice around the Mertz Glacier region, East Antarctica, are included.

Monitoring snow cover variability in an agropastoral area in the Trans Himalayan region of Nepal using MODIS data with improved cloud removal methodology

Satellite aerosol remote sensing entered a new era with the deployment of advanced satellite imaging instruments such as the Moderate Resolution Imaging Spectroradiometer (MODIS) on the NASA Terra and Aqua satellites. These new instruments provide the opportunity to learn more about aerosol properties than was possible using the simpler NOAA Advanced Very High Resolution Radiometer (AVHRR), which has been used to retrieve aerosol optical thickness for more than 20 years. Combining historical AVHRR and the more advanced MODIS aerosol retrievals to form a long‐term aerosol data record is critical for studying aerosol climate forcing. To achieve this objective, it is necessary to build a connection and establish consistency between the two retrievals through a careful evaluation of the two retrieval methods applied to the same data. As a first step in this effort, this paper exploits the potential of the Clouds and the Earth's Radiant Energy System (CERES) Single‐Scanner Footprint (SSF) data set that includes aerosol products derived from Terra MODIS data at the same locations using both the multichannel MODIS and the two‐channel AVHRR aerosol retrieval algorithms. The analysis examines the differences in the results seen over oceans on a global scale. It was found in a global mean sense that advancement in the aerosol retrieval over ocean from the MODIS algorithm relative to the AVHRR method is realized mostly in the improvement of the aerosol size parameter (ASP) rather than in the aerosol optical thickness (AOT). However, regional differences were observed in both AOT and ASP retrieved from the MODIS and AVHRR algorithms. These are examined further in the second part of this two‐part paper. Cloud contamination and surface roughness appear to affect both aerosol retrievals, effects that need further investigation.

Vegetation indices (VIs) such as the Normalized Difference Vegetation Index (NDVI) are widely used for assessing vegetation cover and condition. One of the NDVI's significant disadvantages is its sensitivity to aerosols in the atmosphere, hence several atmospherically resistant VIs were formulated using the difference in the radiance between the blue and the red spectral bands. The state‐of‐the‐art atmospherically resistant VI, which is a standard Moderate Resolution Imaging Spectroradiometer (MODIS) product, together with the NDVI, is the Enhanced Vegetation Index (EVI). A different approach introduced the Aerosol‐free Vegetation Index (AFRI) that is based on the correlation between the shortwave infrared (SWIR) and the visible red bands. The AFRI main advantage is in penetrating an opaque atmosphere influenced by biomass burning smoke, without the need for explicit correction for the aerosol effect. The objective of this research was to compare the performance of these three VIs under smoke conditions. The AFRI was applied to the 2.1 µm SWIR channel of the MODIS sensor onboard the Earth Observing System (EOS) Terra and Aqua satellites in order to assess its functionality on these imaging platforms. The AFRI performance was compared with those of NDVI and EVI. All VIs were calculated on images with and without present smoke, using the surface‐reflectance MODIS product, for three case studies of fires in Arizona, California, and Zambia. The MODIS Fire Product was embedded on the images in order to identify the exact location of the active fires. Although good correlations were observed between all VIs in the absence of smoke (in the Arizona case R 2 = 0.86, 0.77, 0.88 for the NDVI–EVI, AFRI–EVI, and AFRI–NDVI, respectively) under smoke conditions a high correlation was maintained between the NDVI and the EVI, while low correlations were found for the AFRI–EVI and AFRI–NDVI (0.21 and 0.16, for the Arizona case, respectively). A time series of MODIS images recorded over Zambia during the summer of 2000 was tested and showed high NDVI fluctuations during the study period due to oscillations in aerosol optical thickness values despite application of aerosol corrections on the images. In contrast, the AFRI showed smoother variations and managed to better assess the vegetation condition. It is concluded that, beneath the biomass burning smoke, the AFRI is more effective than the EVI in observing the vegetation conditions.