Determination of Chlorophyll-A Concentration from Seawifs Data in the South China Sea

The use of satellite remote sensing to provide synoptic measurements of the ocean is becoming increasingly important in the fishing industry. The evolving capabilities of satellite sensors and data processing techniques provide a promising tool towards the development of fish forecasting and management techniques. Mapping phytoplankton distribution and growth are important in fisheries and physical oceanographic studies. The light absorbing pigments collectively known as chlorophyll-a are commonly used by oceanographers as an index of phytoplankton concentration. The objective of this study is to measure the concentration of chlorophyll-a in the Exclusive Economic Zone (EEZ) of East Coast Peninsular Malaysia, based on remotely sensed data. In order to achieve this objective it is essential to determine an empirical relation between the chlorophyll-a and the radiances values recorded by the sensor and to measure the concentration chlorophyll-a from remotely sensed data. This study used in-situ data of concentration chlorophyll-a to measure the concentration of chlorophyll-a from SeaWiFS data. Models to estimate the chlorophyll-a concentration were generated by computation based on empirical method using radiance ratio of SeaWiFS channels. The data from the sea truth campaigned of 24th August 2000 until 29th August 2000 were applied to obtain the correlation between chlorophyll-a concentration (mg/m3) and the radiance values in chosen channel of SeaWiFS. The amount of concentration of chlorophyll-a was calculated based on blue, blue-green and green (442nm, 490nm and 555nm) reflectance ratios, this was done by selecting representative radiance values corresponding to in-situ data measurements. The study proved that the remote sensing technique is a very useful tool for studying chlorophyll-a distribution in a large water body area such as the- EEZ. In this work, channel 2, channel 3 and channel 5 of SeaWiFS data have been found to be the most suitable channel to extract the chlorophyll-a concentration. Correlation analysis between remotely sensed data and chlorophyll-a in-situ data indicates the possibility of mapping chlorophyll-a concentration with some degrees of success. The strong correlation of radiance ratio corresponding to above channel with in-situ data provides the basis for the development of equation and constant for the estimation of chlorophyll-a concentration in South China Sea

Identification of initial drift in semiconductor gas sensors caused by temperature variation

Metal-oxide (MOX) gas sensors are well-known with their high sensitivity in detecting gases. Despite of this quality, the responses of gas sensor are inclined to substantial drift effects caused by the environmental variable of the surrounding atmosphere such as temperature. The variation of temperature introduced shifts in the dynamic features of sensor resistance, and nonlinearly modified the original unique patterns of acquired response. In this paper, the initial drift in MOX gas sensors were identified from the responses of gas sensors that shifted over temperature variation. This initial drift identification is important for further analyses on drift compensation

Modification of wavelet transform approach for low-wind direction extraction

Regional wind possession that experienced low wind study gives challenged the researcher in recognizing high spatial behavior of wind. Current practices of wind direction retrieval involved the derivation of wavelet coefficient through wavelet decomposition and wavelet transform in Fourier window of satellite images. However, mentioned technique underestimate wind streak of low wind speed where most of the studies have focueds only at high wind speed area. This study aims to enhance wavelet decomposition through enhancement of multi resolution analysis. The images used in this study covered low wind speed area (3-5 m/s) and consist of two modes of RADARSAT-1 SAR images; Standard-2 and Wide-3 modes. Identification of the most suitable modes for low-wind direction extraction signifies the use of two types of modes. Fast Fourier Transform function was applied on wavelet coefficient window of RADARSAT-1 SAR data. The extension work was validated using Quikscat wind direction data and it agrees with the method with r-squared values of 0.6233 for Standard-2 and 0.6483 for Wide-3 images. The extension of the study has potential application in the extraction of wind direction in low wind speed area

Seasonal wind speed distribution analysis in west coast of Malaysia

Wind in Malaysia varies according to the Northeast and Southwest monsoon. The transition period of the two monsoons, April and October inter-monsoon also influence the wind in Malaysia. The determination of the fit wind speed distribution has become a vital process in wind energy estimation and coastal engineering application. However, previous study focuses only on the fit annual distribution instead of the fit seasonal distribution of wind speed. The fit seasonal distribution of wind can leads to the proper installation of wind energy technology devices, the wind power generation and the pattern of the wind itself. Thus, this paper aims to determine the best fir distribution of monsoon and inter-monsoon occurred in Malaysia every year. The distribution that was tested is the Gamma, Log-normal and Weibull distribution model hence, the fit distribution was determined using Kolmogorov-Smirnov goodness-of-fit test. It was found that the Log-normal distribution fits best with all monsoon and inter-monsoon in Malaysia

Operational peat swamp spatial sensitivity model development

Large-scale patterns of peat swamp forest (PSF) biodiversity have until now been obscured by a sparse and scattered inventory record. Known as edaphic forest, it existed in highly acidic soil and waterlogged condition. PSF had been degraded due to various anthropogenic purposes and the impact is largely affected on species level. This fragile forest is facing constant threats at alarming rate and the need of sensitivity study at landscape level is crucial in order to reduce the disturbance impact in PSF area. Here we present the first comprehensive sensitivity spatial model based on disturbance level of tree compositions for PSF in Pekan, Pahang. Data from the hyperspectral imaging will be integrated with ground measurement data to delineate tree PSF zoning and determine PSF the sensitivity levels. PSF spatial sensitivity model is simulated on combination parameters which derive from land cover/land use mapping, physical factors, and tree species composition based on spatial ecology software with integrated GIS features. Using spatial ecology modeling, the PSF spatial sensitivity zoning will be linked into geographic database. Initial sampling design decisions in PSF sensitivity studies using observational field assessment influence the ability to detect and accurately estimate the impacts. As the fragile PSF is high in sensitivity and any slight disturbance natural elements may cause it vulnerable to vast destruction areas. Sensitivity modeling on entire ecosystem is important to investigate the sensitivity level of ecosystem due to changes nearby. The model developed can be used to assess the fragility of PSF ecosystem due to physical changes and surrounding. Later, model can be used as indicator for forest conservation and help in preventing and monitoring vulnerable area of PSF

Image-based atmosphere correction using dark pixel subtraction technique in Penang Island, Malaysia / Wan Noni Afida Ab Manan, Arnis Asmat and Noordin Ahmad

Lack of study has found in emphasizing the appropriate chosen of atmospheric models with specific atmospheric condition. This study is attempting to answer whether selection of atmospheric models is based on regional atmospheric condition or geographic location. The proposed method is a combination of the radiative transfer equation and dark target subtraction technique. Two important atmospheric parameters in the radiative transfer equation which are visibility and aerosol loading are estimated from the image itself to be as an input in atmospheric modelling. ATCOR-2 was used to perform different atmospheric models (maritime and urban) which can represent regional climatic condition in Penang Island, Malaysia. By relating the determined aerosol optical thickness with visibility values, urban model at the visible (blue band) on image 2005 showed a high correlation coefficient which is r2 = 0.8896. It has been shown that determined the aerosol is highly correlated to the visibility range from 10 to 50 km. Study also found that optical satellite remotely sensed image data (Landsat TM blue band) can be used to determine the visibility value through the darkest pixel atmospheric correction algorithms

Wind direction extraction from synthetic aperture radar (SAR) using wavelet transform technique

Backscatter of RadarSat-1 SAR images for incidence angles between 20° to 70° at an ocean area is caused by Bragg scattering. The Bragg-scale waves created based on the response of the ocean to the wind stress. Therefore, wind direction can be retrieved in radar images from the orientation of the wind streaks that visible in the images. However, the variation of the incidence angle can cause geometric distortion and variation in scattering components. SAR images for Wide-3 and Extended-High 6 modes have produced wind direction which similar as recorded in AWAC data with correlation are r=0.94 and r=0.98respectively. The wind blows for both images is correspond during North East Monsoon (September to March) with wind speed about 0.9 m/s. However, weak correlation is exhibits for Standard-2 (r=0.29), it may due to wide range of incidence angle that slow wind speed become invisible to the wavelet formation. From the result, it shows that Extended High-6 mode is considered the best mode to make use for extracting wind direction with high correlated with AWAC data. This is also confirmed that large incident angle with small range angle provides more information on wind direction, as Extended High-6 having the largest incidence angle among the two modes. As conclusion, the SAR backscatter is closely affected by the incidences angles, and this can provide on wind direction information for wind studies

Temperature drift identification in semiconductor gas sensors

The efficiency of metal-oxide (MOX) semiconductor gas sensor is depends on the high accuracy of its performance. In real monitoring situation, the responses of gas sensor are inclined to substantial drift effects that caused by environmental factors (i.e., ambient temperature and humidity) that have reduced the sensor's accuracy. Therefore, the study aims to identify the probable span of drift in sensor responses that was introduced by ambient temperature variation. Two gas sensors (TGS2600 and TGS2602) were used to observe the drift due to ambient temperature variation (25, 30, 35 and 40°C) in exposure of clean air and 6 ppm toluene. The ambient temperature of 25 °C was set as the starting temperature for drifting point, and used as the baseline for identification of drift occurrence. The probable span of drift was later translated into percentage for easy interpretation. Results show that the sensors resistances were drifted in a wide range with their respective drift percentage as the ambient temperature were increased. The resistances for TGS2600 and TGS2602 were drifted up to 57.61 and 61.21 % in clean air while 40.13 and 9.7 % in 6 ppm toluene, respectively. It can be concluded that the probable span of drifted responses has been identified for TGS2600 and TGS2602 in clean air and 6 ppm toluene due to the variation of ambient temperature beyond 25 °C

An exploratory study on wind speed profiling of high-rise building/monument using EnviMET.

Envi-MET is a useful tool for simulating wind speed at building heights and modelling microclimatic conditions around buildings, including wind speed around buildings and other structures. Envi-MET is used in this study to simulate wind speed toward building heights. When R2 = 0.8186, relative bias is -0.0775, and RMSE is 0.2578, the agreement between Envi-MET simulation and ground observation indicates acceptable agreement. With this establishment, it was discovered that the building's height and wind speed are not the only factors causing destruction; the less friction of wind with surface features will also increase the wind speed, as shown by the results of the vertical profile wind speed in relation to the tollway building's height. At a height of 13 metres, the wind speed is 3.5 m/s. Wind circulation affects the building at this elevation, causing damage to the roof and ceiling. Buildings and structures can sustain significant damage as a result of high wind speeds. When wind speeds are high, the wind's force increases, causing pressure differences on different sides of a building or structure. The findings of this study inform relevant parties of the impact of wind on building construction and how it may influence variations in wind speed