Showing papers by "Feifei Pan published in 2016"

Forest above Ground Biomass Inversion by Fusing GLAS with Optical Remote Sensing Data

Abstract: Forest biomass is an important parameter for quantifying and understanding biological and physical processes on the Earth’s surface. Rapid, reliable, and objective estimations of forest biomass are essential to terrestrial ecosystem research. The Geoscience Laser Altimeter System (GLAS) produced substantial scientific data for detecting the vegetation structure at the footprint level. This study combined GLAS data with MODIS/BRDF (Bidirectional Reflectance Distribution Function) and ASTER GDEM data to estimate forest aboveground biomass (AGB) in Xishuangbanna, Yunnan Province, China. The GLAS waveform characteristic parameters were extracted using the wavelet method. The ASTER DEM was used to compute the terrain index for reducing the topographic influence on the GLAS canopy height estimation. A neural network method was applied to assimilate the MODIS BRDF data with the canopy heights for estimating continuous forest heights. Forest leaf area indices (LAIs) were derived from Landsat TM imagery. A series of biomass estimation models were developed and validated using regression analyses between field-estimated biomass, canopy height, and LAI. The GLAS-derived canopy heights in Xishuangbanna correlated well with the field-estimated AGB (R2 = 0.61, RMSE = 52.79 Mg/ha). Combining the GLAS estimated canopy heights and LAI yielded a stronger correlation with the field-estimated AGB (R2 = 0.73, RMSE = 38.20 Mg/ha), which indicates that the accuracy of the estimated biomass in complex terrains can be improved significantly by integrating GLAS and optical remote sensing data.

Trends in agricultural heat and solar radiation resources in Northeast China: A multistage spatio‐temporal analysis

Abstract: Climate change has changed the distribution of climate resources in crop growing season, and caused some impacts on agricultural production. Based on daily meteorological data collected at 71 meteorological stations in Northeast China, trends at multi-temporal scales (decadal, annual, monthly, and 10-day) and spatial patterns of heat resources [temperature, frost-free period (FFP)] and solar radiation resources [growing season's sunshine hour (GSS)] are estimated over the period 1961–2012. The period of 2000–2012 has been successively warmer than the previous decades with higher mean values for both temperature and FFP, and temperature had an abrupt increasing change in the 1980s. An increasing trend was identified for the daily mean temperature in the study area, with the trend value (0.30 °C decade−1) double the global warming rate (0.14 °C decade−1). As the last frost date advanced by 1.9 days decade−1 in spring and the first frost date delayed by 1.6 days decade−1 in fall, FFP increased by 17.9 days in recent 52 years with the average trend value of 3.5 days decade−1. Temperature in February exhibited the highest increasing rate; furthermore, the maximum temperature trends occurred in the last 10 days of February at most stations. Daily sunshine hours decreased in June, July, and August, but GSS showed small changes at decadal and annual scales because of the prolonged FFP. In summary, climate change has prolonged FFP, increased the heat resource, and slightly changed solar radiation resource during crop growing season, which is beneficial for agriculture in Northeast China.