APPLICATIONS OF MODERATE-RESOLUTION REMOTE SENSING TECHNOLOGIES FOR SURFACE AIR POLLUTION MONITORING IN SOUTHEAST ASIA

Retrievals from Earth observation satellites are widely used for many applications, including analyzing dynamic lands and measuring atmospheric components. This research aims to evaluate appropriateness of using satellite retrievals to facilitate understanding characteristics of Southeast Asian (SEA) surface air pollution, attributed to regional biomass burnings and urban activities. The studies in this dissertation focused on using satellite retrievals for 1) mapping potential SEA air pollution sources; which are forests, rice paddies, and urban areas, 2) understanding dynamic optical characteristics of SEA biomass-burning aerosols, and 3) inferring surface ozone level. Data used in this study were from three NASA\u27s Earth Observing System (EOS) satellites, which are Terra, Aqua, and Aura. These retrievals have spatial resolution ranging from hundred meters to ten kilometers. Algorithms used for the SEA land cover classification were developed using time-series analyses of surface reflectance in multiple wavelength bands from Moderate Resolution Imaging Spectroradiometer (MODIS) on the Terra satellite. Comparing the results to national statistical databases, good agreement was obtained for spatial estimation of forest areas after correction with plantation areas. For estimation of rice paddies areas, the agreement depended on the rice ecosystems. It was good for rainfed rice and poor for deepwater rice. Models for irrigated and upland rice areas showed overall high coefficients of determination, suggesting that they effectively simulated the spatial distribution of those rice paddies; but were prone to underestimate and overestimate, respectively. Estimated SEA regional rice area was 42×106 ha, which agrees with previous published values. Analysis of the satellite retrieval could identify large urban areas. However, the satellite-derived urban areas also incorrectly included large sandy beaches. Optical properties of SEA background aerosols were investigated through the multivariate analyses of long-term ground-based aerosol measurements acquired from Aerosol Robotic Network (AERONET). The results in this study showed that from mid-September to December, the aerosol had both fine size and high light scattering efficiency. It was assumed to be largely urban/industrial aerosols, possibly coming from eastern China. From January to April, the aerosol had fine size and had single scattering albedo (SSA at 440 nm) of approximately 0.9. It was assumed to be smoke from local biomass burning. From October to January, when seasonal winds are strongest, more SEA urban aerosol was observed. This aerosol had coarser size and had SSA of ~0.9 or less. The appropriateness of using Ozone Monitoring Instrument (OMI) aerosol retrieval to facilitate understanding SEA biomass-burning aerosol properties was evaluated through three lines of evidence. These are 1) comparisons between the results obtained from multivariate analyses of the OMI aerosol retrieval and those obtained from the ground-measured AERONET data, 2) from Atmospheric Infrared Sounder (AIRS) total column CO product, and 3) from MODIS active fire detections. The results showed that the OMI retrieval used for large-scale SEA biomass-burning aerosol characterization was consistent with these alternative measures only when 1 \u3c OMI aerosol optical depth (442 nm) \u3c 3. The OMI aerosol retrieval was then used for the study on dynamic characteristics of biomass burning aerosol. This study considered the aerosols from two forest-fire episodes, 2007 SEA continent and 2008 Indonesian fires. Dependence of the aerosol optical properties on four variables was investigated. These variables were 1) wind speed/direction, 2) relative humidity (RH), 3) land use/cover as a surrogate of fuel type estimated from time-series analysis of MODIS surface reflectance, and 4) age of aerosol estimated from spatial-temporal analysis of MODIS active fire and the wind characteristics. Results from Pearson Chi-square test for independence showed that the dependence between aerosol group memberships with different optical properties and the limiting variables was significant for most cases, except for Indonesian aerosol age factor. These results agree with prior knowledge on regional burning conditions (types of fuel and relative humidity) and aerosol chemical/physical properties (chemical composition related to aerosol optical properties and hygroscopicity). Using EOS-Aura tropospheric column ozone (TCO) to infer surface ozone level was evaluated through analyses of linear relationships between TCO estimated from OMI and Microwave Limb Sounder (MLS) retrievals and coincident TCO from balloon-based ozonesonde measurements. This evaluation was for different tropospheric ozone profile shapes and for different geographical regions (for low, mid, and high latitudes and for Pacific and Atlantic regions). Results indicate that inference on ozone level derived from the satellite-based TCO requires corresponding information about tropospheric ozone profile shape. The use of satellite-based TCO was more appropriate for polluted low-latitude locations where upper troposphere ozone is rare and surface enhanced ozone is high

Multi-decadal trends and oscillations of Southeast Asian monsoon rainfall in northern Thailand

Understanding the rainfall patterns in northern Thailand is crucial for national water management since they affect several of Thailand’s major rivers. This study aims to understand the trends of climatic variations in northern Thailand over the past 64 years (1951-2014). Pre- and post-monsoon rainfalls are considered to assess temporal Southeast Asian monsoon (SEAM) transition. Finally, multi-decadal oscillations of the rainfalls were evaluated using the Holt-Winters seasonal time-series analysis and their associations with the biennial oscillation, El Niño Southern Oscillation (ENSO), Indian Ocean Dipole (IOD), MaddenJulian Oscillation (MJO), and the Schwabe-Hale cycle were also discussed. The results showed a climatic trend toward earlier coming of the SEAM rainfall. The time-series and linear correlation analyses revealed that the ENSO, MJO, and solar irradiance influenced the rainfalls differently in the pre- or post-SEAM or both and they were also related to the periodicities of the extreme rainfall events. However, the IOD did not directly influence the local SEAM rainfall but it co-occurred with the ENSO

Northward expansion of paddy rice in northeastern Asia during 2000-2014.

Paddy rice in monsoon Asia plays an important role in global food security and climate change. Here we documented annual dynamics of paddy rice areas in the northern frontier of Asia, including Northeastern (NE) China, North Korea, South Korea, and Japan, from 2000-2014 through analysis of satellite images. The paddy rice area has increased by 120% (2.5 to 5.5 million ha) in NE China, in comparison to a decrease in South Korea and Japan, and the paddy rice centroid shifted northward from 41.16 °N to 43.70 °N (~310 km) in this period. Market, technology, policy, and climate together drove the rice expansion in NE China. The increased use of greenhouse nurseries, improved rice cultivars, agricultural subsidy policy, and a rising rice price generally promoted northward paddy rice expansion. The potential effects of large rice expansion on climate change and ecological services should be paid more attention in the future

Soil and biomass carbon stocks in forest and agricultural lands in tropical climates

This study aims to assess the carbon storage capability of dominant vegetative land covers in Thailand by estimating biomass, biomass carbon and soil carbon stocks. Above-ground biomass was estimated from allometric equation or actual raw yield. Soil organic carbon was analyzed according to the Chromic acid titration method. Results show that above-ground biomass carbon for irrigated rice, sugarcane, mature Para rubber, degraded rain forest and mixed deciduous forest were 0.8- 1.3, 11.1, 91.5, 56.6 and 60.5 tonne C ha-1, respectively; whereas topsoil carbon at 0-30 cm were 14.9-21.3, 11.3-13.8, 34.2, 54.6 and 77.7-136.9 tonne C ha-1, respectively. Additional studies on the roles of leaf litters involving soil carbon and effects of agricultural practices on carbon storage capability should be considered. Furthermore, advantages of bio-fuel over the lost organic carbon in agricultural systems and decline in crop yield could be also taken into account

Diurnally-micrometeorological responses to different vegetation cover in a highly-deforested tropical area in Nan, Northern Thailand, during the early Asian summer monsoon

This work aims to investigate diurnal-micrometeorological patterns for different vegetation covers; a hill evergreen forest, an integrated cropland, and a monoculture cropland in Nan, Northern Thailand. Biogeophysical effects of deforestation and cropland expansion on the local meteorological patterns are discussed. Results obtained from the analysis of satellite imagery suggest significant forest conversions from year 2001 to 2011/12. Field observations were taken during the early Asian summer monsoon season. The results indicate that the forest exhibited the highest day-night temperature difference, in which latent heat flux and surface roughness, in connection with wind speed, play important roles. Different cultivation practices (monoculture vs. integrated) clearly affected daytime sensible heat flux, resulting in colder nights at the monoculture cropland. Based on the findings in this study, an overall warming trend, especially at night, and higher short-term rainfall are likely to be associated with deforestation and cropland expansions

Preliminary assessment of land–air energy transfers in tropical forest and agro-ecosystems

This study aims to show preliminary results of meteorology and surface energy transfers in tropical forests and agroecosystems and their associations with vegetation canopy and soil water content. Field observations were conducted at the selected vegetation sites and adjacent sparse vegetation sites in the Northeast of Thailand from the summer season to early rainy season. The study results showed that diurnal variations on spatial soil temperature gradient between bare soil and vegetation soil was significant but not much for air temperature and humidity. Influenced by season and cropping cycle, soil water content (SWC) could induce greater spatial air temperature and humidity differences and moderated the spatial soil temperature gradient. Among various vegetation covers, diurnal patterns on energy transfers and associations between SWC and latent heat were clearly different and they suggest substantial microclimate changes associated with the conversion of forests into croplands

CBCT-to-CT Translation Using Registration-Based Generative Adversarial Networks in Patients with Head and Neck Cancer

Recently, deep learning with generative adversarial networks (GANs) has been applied in multi-domain image-to-image translation. This study aims to improve the image quality of cone-beam computed tomography (CBCT) by generating synthetic CT (sCT) that maintains the patient’s anatomy as in CBCT, while having the image quality of CT. As CBCT and CT are acquired at different time points, it is challenging to obtain paired images with aligned anatomy for supervised training. To address this limitation, the study incorporated a registration network (RegNet) into GAN during training. RegNet can dynamically estimate the correct labels, allowing supervised learning with noisy labels. The study developed and evaluated the approach using imaging data from 146 patients with head and neck cancer. The results showed that GAN trained with RegNet performed better than those trained without RegNet. Specifically, in the UNIT model trained with RegNet, the mean absolute error (MAE) was reduced from 40.46 to 37.21, the root mean-square error (RMSE) was reduced from 119.45 to 108.86, the peak signal-to-noise ratio (PSNR) was increased from 28.67 to 29.55, and the structural similarity index (SSIM) was increased from 0.8630 to 0.8791. The sCT generated from the model had fewer artifacts and retained the anatomical information as in CBCT

Trends of Runoff Variation and Effects of Main Causal Factors in Mun River, Thailand During 1980–2018

Mun River is the largest tributary of the Mekong River in Thailand and provides abundant water resources not only for an important agricultural area in Thailand but also for the lower Mekong River. To understand how the runoff of Mun River responds to climate change and human activities in recent decades, this study performed a detailed examination of the characteristics of runoff variation based on measurements at two hydrological gauging stations on the main stem of Mun River during 1980–2018. Using the Mann-Kendall test, Morlet wavelet transform and Double Cumulative Curve methods, this study identifies that the variation of annual runoff of Mun River encountered an abruption in 1999/2000, with an increased trend taking place since then. Furthermore, a detailed assessment of the effects of the variations in rainfall, temperature, evaporation, and land use types extracted from remote sensing images at the basin scale reveals that a significant reduction in forest area and slight reductions in evaporation and farmland area taking place since 1999 can lead to an increase in the runoff of Mun River, while the dramatic increase in garden area since 1999 tends to make the runoff decrease

Water Quality of the Mun River in Thailand—Spatiotemporal Variations and Potential Causes

The water quality of the Mun River, one of the largest tributaries of the Mekong River and an important agricultural area in Thailand, is investigated to determine its status, identify spatiotemporal variations and distinguish the potential causes. Water quality dataset based on monitoring in the last two decades (1997–2017) from 21 monitoring sites distributed across the basin were analyzed using seasonal Kendall test and water quality index (WQI) method. The Kendall test shows significant declines in fecal coliform bacteria (FCB) and ammonia (NH3) in the upper reaches and increases in nitrate (NO3) and NH3 in the lower reaches. Strong temporal and spatial fluctuations were observed in both the concentrations of individual parameters and the WQI values. Seasonal variation of water quality was observed at each monitoring site. WQI values in August (flood season) were generally among the lowest, compared to other seasons. Spatially, sites in the upper reaches generally having lower WQI values than those in the lower reaches. Excessive phosphorus is the primary cause of water quality degradation in the upper reaches, while nitrogen is the primary parameter for water quality degradation in the lower reaches. Urban built-up land is an important “source” of water pollutants in the lower basin, while agricultural land plays a dual role, affecting across the basin