Drought is a natural climate phenomenon occurring throughout the world，which is one of the most severe natural hazards that affects the society and brings the economic losses． In recent years，the global climate change and society development increased the degree of drought influence and risk，which brought a great threat to global agriculture，water resourse，ecological environment security and the sustainable development of the society．Thus，to improve the drought monitoring and early warning technology level is the foundation to deal with drought and alleviate the drought vulnerability．Satellite remote sensing technology has made great progress in drought monitoring and plays an irreplaceable role in global drought monitoring and early warning with the development of the earth observation technology in recent thirty years． However，it is not enough to provide support for drought disaster prevention and mitigation，for the drought is a complex problem needed interdisciplinary study，and its spatial and temporal characteristics differences are greatly．In this paper，we reviewed and summarized the drought monitoring technology of satellite remote sensing，evaluated and discussed the various problems existing in remote sensing drought indices and models，indicated the main technical problems of satellite remote sensing drought monitoring and the future development opportunities，and put forward the main problems to be solved and the direction should effort in view of the current situation of China s satellite remote sensing drought application．
Abstract: The reflectance spectra were measured of some featured crops and typical vegetation with the ASD Handheld FieldSpec spectrometer FR2500 in Gansu province． By the computer programming technology，the spectra database of typical ground objects in northwest China was set up． This paper mainly introduces spectrum data collection，the establishment course of database system，application and problems of database．
The interpolation of air temperature is one of the most important methods in generating high spatial resolution data for un known points. However, many traditional interpolation methods without geographical information considered were mostly mathematic ways. The paper, based on digital elevation model (DEM) and the monthlymean air temperature collected from 82 stationswhich loca ted in and around the eastern regions of Gansu, p roposed a multip le linear regression spatial interpolation (MLR) method via analyzing the relationship s ofmean air temperature with latitude, longitude, altitude, slope and aspect, and meanwhile carried out the compari son ofMLR with conventionalmethods such as Inverse Distance Squared method ( IDS) , Sp line method ( SPL INE) and Ordinary Krig ing method (OK) , which showed that the p recision ofMLR method taking into account terrain factorswas better than that of other con ventionalmethods. Finally, using theMLR method, a data set ofmonthlymean air temperature with 84 m ×84 m spatial resolution in the eastern regions of Gansu was obtained, which exhibited that the spatial distribution ofmonthlymean air temperature in the eastern regions of Gansu, p resented the zonal rule which decreased from the southeast to the northwest, and the extent and trend of fluctuation with mean air temperature in season internally was different, that is, the lowest undulation extentwas in summer, then in winter, and the undulation range in sp ring and fallwas the biggest, and the trend of fluctuation p resented the latitudinal zonal from the west to east in summer, the north to south in winner, the southwest to northeast in sp ring and fall.
The photo—·physiological characteristics of Achnatherum splendens both in the enclosure an d the grazing pasture were moni-toted in Anxi．Th e results showed that the diference was significant between them．Th e air temperature and leaf temperature were rela．tively lower and the relative humidity Was higher in the enclosure compared with those in the grazing grassland．These indicated that the environment of grass growth Was greatly improved by enclosure means．At the same time，there Was higher photosynthetic rate of Ach-hat．rum splendens in the enclosured grassland．This Was beneficial to growth of grass and accumulation of dry matter．
Using TERRA ／MODIS data in some typical vegetation regions during plant growth period in 2003 and vegetation type data，the sDatial and temporal characteristics of MODIS／NDVI and MODIS／EVI in Northwest China an d the influences of atmosphere con'ec-ti0n on the two vegetation indexes were an alyzed in this paper for comparing the diferences between NDVI and EVI．The results show that distributi0ns of NDVI an d EVI are consistent in space and nearly the same as that of precipitation．Th e diference between NDVI and EVI is larger as vegetation coverage increases．In addition．the infl uence of atmosphere on NDVI and EV1 was obvious，and atmos-DheIle c0n．ecti0n made NDVI values increase and EVI values reduce；the values of NDVI are smaller than those of EVI before atmos--DheIle c0rrecti0n：while after the correction，values of NDVI are larger than those of EVI in most regions． By comparing NDVI and EVI in th0se regi0ns containing more aerosols．we found that EVI had a good performance in removing the infl uence 0l aerosols．
By analyzing spectrum characteristics of snow，clouds and diferent land covers in the Qilian Mountain region based on MO-DIS data from July 2003 to March 2005，a new method for snow discrimination is presented on the basis of former researches，which combined NDSI(Normalized Diference Snow Index)and band 18，band 3 1 of MODIS to discriminate snow from clouds，saline，ice，desert，etc．with a step—by—step approach．Both result analysis and examination show that snow in the Qilian Mountain region canbe efectively discriminated by the method of this article．
Using TERRA ／MODIS data in some typical vegetation regions during plant growth period in 2003 and vegetation type data，the sDatial and temporal characteristics of MODIS／NDVI and MODIS／EVI in Northwest China an d the influences of atmosphere con'ecti0n on the two vegetation indexes were an alyzed in this paper for comparing the diferences between NDVI and EVI．The results show that distributi0ns of NDVI an d EVI are consistent in space and nearly the same as that of precipitation．Th e diference between NDVI and EVI is larger as vegetation coverage increases．In addition．the infl uence of atmosphere on NDVI and EV1 was obvious，and atmos DheIle c0n．ecti0n made NDVI values increase and EVI values reduce；the values of NDVI are smaller than those of EVI before atmos-DheIle c0rrecti0n：while after the correction，values of NDVI are larger than those of EVI in most regions． By comparing NDVI and EVI in th0se regi0ns containing more aerosols．we found that EVI had a good performance in removing the infl uence 0l aerosols．
The S110rtagP Of WatPT TPSOLITCPS 1S a SPTIOLIS pT Oh1Pm partlCLIlaTly In f.hlna. Nlanaglng WatPT TPSOLITCPS On the haS1S Of PVapOtTanSplTatlOn(ET}, TPtT1PVPd malnly from SatPlhtP TPmOtP SPriSlng, 1S a nPW COriCPpt 1ntT0(1LICPd In the CEF Hal hTO}PCt On COmpTP11PriS1VP management Of WatPT TPSOLnCPS and PriV1TOnmPnt. rfhP mOSt pOpLIlaT TPmOtP SPriSlng afgOTlthmS In the TPtT1PVa1 Of ET aTP TPV1PWPd. Among them the SEBAL }SLII}}aCP EriPTgy BalanCP A1gOTlthm fOT Lan(1} haS hPttPr phySlCa1 haC1}gTOlln(1 and Keen LISPd OpPTatlOnally In many COLIntT1PS In last IO yPaTS. Data from the NIOI}PTatP TPSOhltlOn Imaglng CtTOTadlOmPtPT }NIOI}IS} and LandSat TNI} ErfNI+ have Keen LISPd t0 PVa1LIatP (lady, SPa.SOnal and annllaf ET pPT COllnty and pPT land LISP Category. A pTPhmlnary analySlS for the Hai Basin, for 2002, is presented. Further studies will he continued for the Hai River Basin over next five years, which will pTOV1dP a TPfPTPriCP fOT the apphCatlOn Of haSln SCa1P Water LISP tPChnOlOg1PS, In partlCLIlaT, the real Sa.Vlng Of Water TPSOLITCPS by the reduction of ET. In the understanding of the limits of SEBAL, an independent validation program, including precise in situ flux OhSPrVatlOriS, 1S t0 he OpPTatPd In the Hal Ba.Sln hrO}PCt. FOT demnnStratlnn pPT10(1S, WP have tT1Pd t0 LISP n1PSOSCa.}P atmOSphPT1C m0(1P1S, SLICK aS MMS, t0 get the mPtPOTOlOglCaf f1P1dS nPa.T SLII}}aCP, arid help SEBAL In 1tS CalClllatlOn Of SLII}}aCP f1LIXPS. The Ina}Or taSl} 1S the PStahhShmPnt Of a real Water Sa.Vlng pTOgTam thTOllgh an ET TP(1LICtlOn Strategy, Wlth mOTP Water TPSOLITCPS TPmalnlng In the haSln fOT pT0(1LICtlOn and PriV1TOnmPntal LISP, 1nCllldlng mOTP fTPS11WatPT d1SChaTgPS lnt0 the BOhal Sea. ET TP(1LICtlOn 1S land LISP arid CTOp type dependent. Other management faPtnrS afSO need t0 he 1nCh1(1Pd.
In this paper.some research advances on drought monitoring method by remote sensing are introduced. meanwhile.some ｖiews are pointed out and indicated that the drought monitoring should carry out a new way which combine many subjects in the future．
即ectral reflectance characteristic of vegetation was introduced. The advantage and disadvantage of several vegetation index- es in common use were summarized. The characteristics of vegetation monitoring by using MODIS sensor and the two NASA vegeta- tion indexes products and their shortage were indicated. The importance of studying on MODIS vegetation indexes in Northwest China was presented.
