Abstract:
As a frequent natural hazard, drought causes the heaviest damage to daily life and ecological environment among all natural disasters. The large scale and dynamic drought monitoring has been frontier and hot topic in the global climate change and food security research. Satellite remote sensing is the main method of obtaining distributed information of the land surface. However, the applicability of a drought monitoring method varies by region and period. So it's necessary to inspect and evaluate the drought monitoring method to ensure the validity and accuracy in drought monitoring.Vegetation index based
IVC, land surface temperature based and Surface Temperature-Normalized Difference Vegetation Index space (
Ts-
INDV space) based are compared to analyze and evaluate their characteristics and applicability in drought monitoring. The MODIS 16-day NDVI (MOD13A2) and 8-day
Ts (MOD11A2) provided at 1 km spatial resolution as a gridded level-3 product in the Sinusoidal projection are used, and the Heilongjiang Province, the main food production area in China, is chosen as the study area. The monitoring period is from 9 May to 9 June of the year 2000 to 2008. The correlation between
IVC,
ITC,
IVTC and relative soil moisture in 10 cm and 20 cm depth, the correlation between
IVC,
ITC,
IVTC and the precipitation in the satellite monitoring period and the cumulative precipitation in the last 1-, 2-, 3-, 4-period time scales, the difference and the relationship between
IVC,
ITC,
IVTC are analyzed.Significant linear correlation is found between
IVTC and the relative soil moisture in 10 cm and 20 cm depth, especially for the 10 cm depth. The correlation between
IVTC and relative soil moisture is obviously better than that between
ITC,
IVC and the relative soil moisture. So, it can be judged that
IVTC may mirror the soil moisture better than
IVC and
ITC, and is more sensitive to shallow soil moisture.
IVTC is also found linearly correlated with precipitation in current monitoring period, as well as the cumulative precipitation in the last 1-, 2-, 3-, 4-period timescales. The correlations are better than those between
ITC,
IVC and precipitation as well as corresponding cumulative precipitation, which show that
IVTC is more sensitive to precipitation than
IVC and
ITC, and is closely related to not only current precipitation but also past cumulative precipitation. In the early growing season,
IVTC and
ITC are applicable in drought monitoring, while the fractional
IVC cover is too low to monitor drought. It is difficult to compare the drought among different areas with
IVC and
ITC, while based on the energy conservation principle, combining the
INDV and
Ts,
IVTC can reflect soil moisture better and is comparable in different areas. Furthermore, the land surface temperature implied by
IVTC gives more direct hint of drought than the
INDV implied especially on the grassland, then in the crop land, brush land and forest land in sequence.