Urban Thermal Map at Street Level through Advanced Transect Survey
Despite the expectation that small green spaces provide high cooling effects, making air temperatures drop such effect in urban areas has been less explored in comparison to larger parks and urban forests. These knowledge gap has required advanced techniques to record spatial and temporal data and analysis small green spaces cooling effects. A temperature-sensing unit with ventilated double cylinder shelter (TVC) meets the needs and is known as an advanced device to record temperature data more accurately using a T-type thermocouple with a ventilator. This device also can be useful to develop guidance to describe thermal environment with a finer scale and an experimental research design for identifying air temperature data with spatial analysis using TVC. However, how we would conduct transect survey with this device and make a thermal map based on the collected data is not well known. The purpose of the study was to find out the usage of TVCs in collecting air temperature data and was to produce a thermal map of the study site and analyze temperature mitigation effect of each green space. The processes to create a thermal map required complicating, endeavoring and time-consuming works as well as skills to use computer programs for space drawing and spatial analysis. The overview of all the processed to get a thermal map should be helpful for researchers and students. Collected air temperature data and recorded time of them were downloaded, converted to Excel file (XLS) and ready to be analyzed through ArcGIS 9. In the mean time, recorded transect routes were drawn on the site map as polylines and made into spatial points through AutoCAD 2007. The routes consisted of five routes classified into the lawn, the rain garden, the residence, the prairie, and the forest. Separately, each route was drawn because it should reflect its spatial and temporal specification as for when the measurement was conducted. The spatial points of each route created by AutoCAD were converted to shape files (*.shp) and added fields of air temperature and time data in their attribute tables through ArcGIS. This work was done in each measurement hour and day. To create a thermal map, were shape files of each measurement time and the boundary of the site required. IDW (Inverse Distance Weighted) in ArcGIS was analyzed for each measurement hour (10h, 13h, 16h and 19h (20h)). In each analysis, the spatial points of measured air temperature were calculated to get an isotherm distribution for the measurement hour which we call a thermal map. The thermal maps show the air temperature distribution at 10h, 13h, 16h, and 20h. They also can show how land covers have an impact on the change of air temperature on their point and the surrounding areas. The air temperature of the prairie raises up in the morning (21℃) and continues to be cool during the day and after sunset. Meanwhile, the lawn starts at lower air temperature and goes to hotter. The residence is kept lower in its air temperature by big trees. The rain garden and the forest seem to have more time to discuss on why they are not sure their cooling effects.