Cross-calibration of brightness temperature obtained by FY-3B/MWRI using Aqua/AMSR-E data for snow depth retrieval in the Arctic

This study cross-calibrated the brightness temperatures observed in the Arctic by using the FY-3B/MWRI L1 and the Aqua/AMSR-E L2A.The monthly parameters of the cross-calibration were determined and evaluated using robust linear regression.The snow depth in case of seasonal ice was calculated by using parameters of the crosscalibration of data from the MWRI Tb.The correlation coefficients of the H/V polarization among all channels Tb of the two sensors were higher than 0.97.The parameters of the monthly cross-calibration were useful for the snow depth retrieval using the MWRI.Data from the MWRI Tb were cross-calibrated to the AMSR-E baseline.Biases in the data of the two sensors were optimized to approximately 0 K through the cross-calibration,the standard deviations decreased significantly in the range of 1.32 K to 2.57 K,and the correlation coefficients were as high as 99%.An analysis of the statistical distributions of the histograms before and after cross-calibration indicated that the FY-3B/MWRI Tb data had been well calibrated.Furthermore,the results of the cross-calibration were evaluated by data on the daily average Tb at 18.7 GHz,23.8 GHz,and 36.5 GHz(V polarization),and at 89 GHz(H/V polarization),and were applied to the snow depths retrieval in the Arctic.The parameters of monthly cross-calibration were found to be effective in terms of correcting the daily average Tb.The results of the snow depths were compared with those of the calibrated MWRI and AMSR-E products.Biases of 0.18 cm to 0.38 cm were observed in the monthly snow depths,with the standard deviations ranging from 4.19 cm to 4.80 cm.

Utilizing a new soil effective temperature scheme and archived satellite microwave brightness temperature data to estimate surface soil moisture in the Nagqu region, Tibetan Plateau of China

Since the early 2000s, many satellite passive microwave brightness temperature （BT） archives, such as the Advanced Microwave Scanning Radiometer for the Earth Observing System （AMSR-E） BTs, have become the useful resources for assessing the changes in the surface and deep soil moistures over both arid and semi-arid regions. In this study, we used a new soil effective temperature （T scheme and the archived AMSR-E BTs to estimate surface soil moisture （SM） over the Nagqu region in the central Tibetan Plateau, China. The surface and deep soil temperatures required for the calculation of regional-scale T were obtained from outputs of the Community Land Model version 4.5 （CLM4.5）. In situ SM measurements at the CEOP-CAMP/Tibet （Coordinated Enhanced Observing Period Asia-Australia Monsoon Project on the Tibetan Plateau） experimental sites were used to validate the AMSR-E-based SM estimations at regional and single-site scales. Furthermore, the spatial distribution of monthly mean surface SM over the Nagqu region was obtained from 16 daytime AMSR-E BT observations in July 2004 over the Nagqu region. Results revealed that the AMSR-E-based surface SM estimations agreed well with the in situ-based surface SM measurements, with the root mean square error （RMSE） ranging from 0.042 to 0.066 m3/m3 and the coefficient of determination （R2） ranging from 0.71 to 0.92 during the nighttime and daytime. The regional surface soil water state map showed a clear spatial pattern related to the terrain. It indicated that the lower surface SM values occurred in the mountainous areas of the northern, mid-western and southeastern parts of Nagqu region, while the higher surface SM values appeared in the low elevation areas such as the Tongtian River Basin, Namco Lake and bog meadows in the central part of Nagqu region. Our analysis also showed that the new T^scheme does not require special fitting parameters or additional assumptions, which simplifies the data requirements for regional-scale applications. This scheme combined with the archived satellite passive microwave BT observations can be used to estimate the historical surface SM for hydrological process studies over the Tibetan Plateau regions.

The deconvolution of lunar brightness temperature based on the maximum entropy method using Chang'e-2 microwave data

A passive and multi-channel microwave sounder onboard the Chang＇e-2 orbiter has successfully acquired microwave observations of the lunar surface and subsurface structure. Compared with the Chang＇e-1 orbiter, the Chang＇e-2 orbiter obtained more accurate and comprehensive microwave brightness temperature data, which are helpful for further research. Since there is a close relationship between mi- crowave brightness temperature data and some related properties of the lunar regolith, such as the thickness, temperature and dielectric constant, precise and high resolution brightness temperature data are necessary for such research. However, through the detection mechanism of the microwave sounder, the brightness temperature data ac- quired from the microwave sounder are weighted by the antenna radiation pattern, so the data are the convolution of the antenna radiation pattern with the lunar brightness temperature. In order to obtain the real lunar brightness temperature, a deconvolution method is needed. The aim of this paper is to solve the problem associated with per- forming deconvolution of the lunar brightness temperature. In this study, we introduce the maximum entropy method （MEM） to process the brightness temperature data and achieve excellent results. The paper mainly includes the following aspects： first, we introduce the principle of the MEM; second, through a series of simulations, the MEM has been verified as an efficient deconvolution method; and third, the MEM is used to process the Chang＇e-2 microwave data and the results are significant.

Improving microwave brightness temperature predictions based on Bayesian model averaging ensemble approach

The choices of the parameterizations for each component in a microwave emission model have significant effects on the quality of brightness temperature （Tb） sim- ulation. How to reduce the uncertainty in the Tb simulation is investigated by adopting a statistical post-processing procedure with the Bayesian model averaging （BMA） ensemble approach. The simulations by the community microwave emission model （CMEM） cou- pled with the community land model version 4.5 （CLM4.5） over China's Mainland are con- ducted by the 24 configurations from four vegetation opacity parameterizations （VOPs）, three soil dielectric constant parameterizations （SDCPs）, and two soil roughness param- eterizations （SRPs）. Compared with the simple arithmetical averaging （SAA） method, the BMA reconstructions have a higher spatial correlation coefficient （larger than 0.99） than the C-band satellite observations of the advanced microwave scanning radiometer on the Earth observing system （AMSR-E） at the vertical polarization. Moreover, the BMA product performs the best among the ensemble members for all vegetation classes, with a mean root-mean-square difference （RMSD） of 4 K and a temporal correlation coefficient of 0.64.

Seasonal and Interannual Variations of Upper Tropospheric Water Vapor Band Brightness Temperature over the Global Monsoon Regions

The upper-troposphere water vapor (UTWV) band brightness temperature (BT) dataset derived from the High-resolution Infrared Radiation Sounder (HIRS) channel 12 of the National Oceanic and Atmospheric Administration (NOAA) polar satellites from 1979 to 1995 is used to analyze the seasonal and interannual variations for the global monsoon regions. Results show that (i) there are three major regions where the UTWV band BT varies significantly with season, i.e., South Asia, the western coastal South-North America tropical region and the low-latitude African region; (ii) UTWV band BT clearly reveals the water vapor temporal/spatial features as well as the atmospheric circulation structure over the low-latitude during the monsoon onset; and (iii) there is a remarkable relationship between the interannual variation of the UTWV band BT over the monsoon regions and the sea surface temperature anomaly in the eastern equatorial Pacific.

Assessing the active-passive approach at variant incidence angles for microwave brightness temperature downscaling

The Terrestrial Water Resources Satellite(TWRS)campaign is a planned Chinese candidate satellite mission,and a one-dimensional synthetic aperture technology will be used,resulting in variant incidence angles for collecting synchronous active-passive observations at L-band,which would make brightness temperature(T_(b))downscaling especially challenging when aiming to improve the spatial resolution of soil moisture measurements.In this study,two active-passive T_(b) downscaling algorithms,the time-series regression(TSR)and spectral analysis(SA)algorithms,are assessed comprehensively based on airborne experimental datasets.The results with data collected during the Soil Moisture Experiment 2002(SMEX02)showed that both approaches could provide a reliable downscaled T_(b) at the same incidence angle.Based on the ground and airborne active-passive observations under variant incidence angles from the Soil Moisture Experiment in the Luan River(SMELR)it can be shown that the linear relationship between T_(b) andσis still robust under the case of variant incidence angles,and T_(b)(both h-and v-pol)is better correlated toσvv for most cases thanσhh.Both downscaling approaches can be applied to active-passive observations under varying incidence angles.Moreover,SA method performed better than the TSR method according to the lower RMSE values and higher correlation.

Daily sea ice concentration product based on brightness temperature data of FY-3D MWRI in the Arctic

A daily sea ice concentration(SIC)product in the Arctic,derived from the brightness temperature(TB)data of the Microwave Radiation Imager(MWRI)sensor aboard on the FY-3D satellite,is described in this paper.The MWRI TB raw swath data were first processed into daily gridded data and then corrected using the Advanced Microwave Scanning Radiometer 2(AMSR2)sensor.An ASI algorithm,which uses daily dynamic tie points,was adopted to calculate daily SIC at 12.5 km polar stereographic projection from January 2018 to June 2020.Our generated MWRI SIC product was compared with the AMSR2 SIC based on the ASI algorithm that uses fixed tie points.For more detailed comparison,we then compared our MWRI SIC with the SIC from the Moderate Resolution Imaging Spectroradiometer(MODIS)data.The mean bias between our MWRI SIC and AMSR2 SIC is 4.24%.The absolute values of biases between the daily MWRI SIC and MODIS SIC range from 0.14%to 10.76%,better than the MWRI SIC product based on the NT2 algorithm published by the Chinese National Satellite Meteorological Center.The results show that our MWRI SIC product has a good quality and can be used as a basic dataset for sea ice extent records.The dataset is available at http://www.dx.doi.org/10.11922/sciencedb.00137.

Difference of brightness temperatures between 19.35 GHz and 37.0 GHz in CHANG＇E-1 MRM： implications for the burial of shallow bedrock at lunar low latitude

Indications of buried lunar bedrock may help us to understand the tectonic evolution of the Moon and provide some clues for formation of lunar regolith. So far, the information on distribution and burial depth of lunar bedrock is far from sufficient. Due to good penetration ability, microwave radiation can be a potential tool to ameliorate this problem. Here, a novel method to estimate the burial depth of lunar bedrock is presented using microwave data from Chang＇E-1 （CE-1） lunar satellite. The method is based on the spatial variation of differences in brightness temperatures between 19.35 GHz and 37.0 GHz （ATB）. Large differences are found in some regions, such as the southwest edge of Oceanus Procellarum, the area between Mare Tranquillitatis and Mare Nectaris, and the highland east of Mare Smythii. Interestingly, a large change of elevation is found in the corresponding region, which might imply a shallow burial depth of lunar bedrock. To verify this deduction, a theoretical model is derived to calculate the ATB. Results show that ATB varies from 12.7 K to 15 K when the burial depth of bedrock changes from 1 m to 0.5 m in the equatorial region. Based on the available data at low lunar latitude （30°N-30°S）, it is thus inferred that the southwest edge of Oceanus Procellarum, the area between Mare Tranquillitatis and Mare Nectaris, the highland located east of Mare Smythii, the edge of Pasteur and Chaplygin are the areas with shallow bedrock, the burial depth is estimated between 0.5 m and 1 m.

Digitizing the thermal and hydrological parameters of land surface in subtropical China using AMSR-E brightness temperatures

Digitizing the land surface temperature(T_(s))and surface soil moisture(m _(v))is essential for developing the intelligent Digital Earth.Here,we developed a two parameter physical-based passive microwave remote sensing model for jointly retrieving T_(s) and m_(v) using the dual-polarized T_(b) of Aqua satellite advanced microwave scanning radiometer(AMSR-E)C-band(6.9 GHz)based on the simplified radiative transfer equation.Validation using in situ T_(s) and m_(v) in southern China showed the average root mean square errors(RMSE)of T s and m_(v) retrievals reach 2.42 K(R^(2)=0.61,n=351)and 0.025 g cm^(−3)(R^(2)=0.68,n=663),respectively.The results were also validated using global in situ T_(s)(n=2362)and m_(v)(n=1657)of International Soil Moisture Network.The corresponding RMSE are 3.44 k(R 2=0.86)and 0.039 g cm^(−3)(R^(2)=0.83),respectively.The monthly variations of model-derived Ts and mv are highly consistent with those of the Moderate Resolution Imaging Spectroradiometer T_(s)(R^(2)=0.57;RMSE=2.91 k)and ECV_SM m_(v)(R^(2)=0.51;RMSE=0.045 g cm^(−3)),respectively.Overall,this paper indicates an effective way to jointly modeling T_(s) and m_(v) using passive microwave remote sensing.

GOES-16 ABI Brightness Temperature Observations Capturing Vortex Rossby Wave Signals during Rapid Intensification of Hurricane Irma(2017)

Geostationary Operational Environmental Satellite-16(GOES-16) Advanced Baseline Imager(ABI) observations of brightness temperature(TB) are used to examine the temporal evolutions of convection-affected structures of Hurricane Irma(2017) during its rapid intensification(RI) period from 0600 to 1800 UTC 4 September 2017.The ABI observations reveal that both an elliptical eye and a spiral rainband that originated from Irma's eyewall obviously exhibit wavenumber-2 TB asymmetries.The elliptical eye underwent a counterclockwise rotation at a mean speed of a wavenumber-2 vortex Rossby edge wave from 0815 to 1005 UTC 4 September.In the following about 2 hours(1025–1255 UTC 4 September),an inner spiral rainband originated from the eyewall and propagated at a phase speed that approximates the vortex Rossby wave(VRW) phase speed calculated from the aircraft reconnaissance data.During the RI period of Irma,ABI TB observations show an on–off occurrence of low TB intrusions into the eye,accompanying a phase lock of eyewall TB asymmetries of wavenumbers 1 and 2 and an outward propagation of VRW-like inner spiral rainbands from the eyewall.The phase lock leads to an energy growth of Irma's eyewall asymmetries.Although the eye remained clear from 1415 to 1725 UTC 4 September,an inner spiral rainband that originated from a large convective area also had a VRW-like outward propagation,which is probably due to a vertical tilt of Irma.This study suggests a potential link between convection sensitive GOES imager observations and hurricane dynamics.

Evaluation of the Long-term Performance of Microwave Radiation Imager Onboard Chinese Fengyun Satellites

Accurate brightness temperature(BT)is a top priority for retrievals of atmospheric and surface parameters.Microwave Radiation Imagers(MWRIs)on Chinese Fengyun-3(FY-3)serial polar-orbiting satellites have been providing abundant BT data since 2008.Much work has been done to evaluate short-term MWRI observations,but the long-term performance of MWRIs remains unclear.In this study,operational MWRI BTs from 2012–19 were carefully examined by using simultaneous Advanced Microwave Scanning Radiometer 2(AMSR2)BTs as the reference.The BT difference between MWRI/FY3B and AMSR2 during 2012–19 increased gradually over time.As compared with MWRI/FY3B BTs over land,those of MWRI/FY3D were much closer to those of AMSR2.The ascending and descending orbit difference for MWRI/FY3D is also much smaller than that for MWRI/FY3B.These results suggested the improvement of MWRI/FY3D over MWRI/FY3B.A substantial BT difference between AMSR2 and MWRI was found over water,especially at the vertical polarization channels.A similar BT difference was found over polar water based on the simultaneous conical overpassing(SCO)method.Radiative transfer model simulations suggested that the substantial BT differences at the vertical polarization channels of MWRI and AMSR2 over water were partly contributed by their difference in the incident angle;however,the underestimation of the operational MWRI BT over water remained a very important issue.Preliminary assessment of the operational and recalibrated MWRI BT demonstrated that MWRI BTs were substantially improved after the recalibration,including the obvious underestimation of the operational MWRI BT at the vertical polarization channels over water was corrected,and the time-dependent biases were reduced.

Geochemical Indications of Possible Gas Hydrates in the Northeastern South China Sea

Gas hydrate, mainly composed of hydrocarbon gas and water, is considered to be a clean energy in the 21st century. Many indicators such as BSRs （Bottom-Simulating Reflections）, which are thought to be related to gas hydrate, are found in the South China Sea （SCS） in recent years. The northeastern part of the SCS is taken as one of the most potentials in the area by many scientists. It is situated in the conjunction of the northern divergent continental margin and the eastern convergent island margin, whose geological settings are much preferable for gas hydrate to occur. Through this study, brightness temperature anomalies recorded by satellite-based thermal infrared remotely sensed images before or within the imminent earthquake, the high content of hydrocarbon gas acid-degassed from subsurface sediment and the high radioactive thermoluminescence value of subsurface sediment were found in the region. Sometimes brightness temperature anomalies alone exist in the surrounding of the Dongsha Islands. The highest content of hydrocarbon gas amounts to 393 μL methane per kilogram sediment and the highest radioactive thermoluminescence value is 31752 unit; their geometric averages are 60.5 μL/kg and 2688.9 unit respectively. What is more inspiring is that there are three sites where the methane contents are up to 243, 268 and 359μL/kg and their radioactive thermoluminescence values are 8430, 9537 and 20826 unit respectively. These three locations are just in the vicinity of one of the highest confident BSRs identified by predecessors. Meanwhile, the anomalies are generally coincident with other results such as headspace gas anomaly in the sediment and chloride anomaly in the interstitial water in the site 1146 of Leg 184. The above-mentioned anomalies are most possibly to indicate the occurrence of gas hydrate in the northeastern SCS.

Two-step method to extract seismic microwave radiation anomaly:Case study of M_s8.0 Wenchuan earthquake

The satellite remote sensing has become a promising technique for detecting earthquake and fault activities. But it is still very difficult to exactly extract the earthquake anomaly from the complicated remote sensing information. This paper presented a two-step method to extract the seismic microwave radiation anomaly related with earthquake, which could eliminate the stable influence of geography, terrain, coversphere and seasons, as well as the random influence of weather. Furthermore the two-step method was applied to analyze the anomaly of Wenchuan earthquake based on the data of AMSR-E. Microwave radiation anomalies were effectively detected related to the main shock and aftershocks. The extracted microwave radiation variation showed general features of three-stage： the positive radiation anomaly appeared around the epicenter in the first stage, quiet variation in the second stage, and abnormal area gradually moved to the epicenter in the third stage. After the main shock the microwave radiation anomalies distributed along the Longmenshan faults, and the epicenters of aftershocks were coincident with the anomaly area in space.

Validation of the “HY-2” altimeter wet tropospheric path delay correction based on radiosonde data

Wet tropospheric path delay （PD） is a highly variable term for the altimeter measurement of a sea surface height, caused by the refraction effect of atmospheric water vapor and cloud liquid water. In order to esti- mate PD values, the ＂HY-2＂ system includes a calibration microwave radiometer （CMR） operating at 18.7, 23.8 and 37 GHz. The PD data of the CMR were compared and validated by coincident radiosonde profiles from ten globally distributed radiosonde stations during October 2011 to August 2012. The temporal interval was 1 h. In order to avoid land contamination, different spatial intervals between these two data sets were tested. The empirical fit function of PD uncertainty and spatial interval was found and extrapolated to the ideal situation that the data of CMR and radiosonde were totally coincident. The stability of the brightness temperature of the CMR and its impact on the PD correction was also studied. Consequently, the uncertainty of the PD algorithm of the CMR was estimated to be 2.1 cm.

A Scheme for Estimating Tropical Cyclone Intensity Using AMSU-A Data

Brightness temperature anomalies measured by the Advanced Microwave Sounding Unit （AMSU） on the National Oceanic and Atmospheric Administration （NOAA） polar-orbiting series are suited to estimate tropical cyclone （TC） intensity by virtue of their ability to assess changes in tropospheric warm core struc-ture in the presence of clouds. Analysis of the measurements from different satellites shows that the variable horizontal resolution of the instrument has significant effects on the observed brightness temperature anoma-lies. With the aim to decrease these effects on TC intensity estimation more easily and effectively, a new simple correction algorithm, which is related to the product of the brightness temperature gradient near the TC center and the size of the field-of-view （FOV） observing the TC center, is proposed to modify the observed anomalies. Without other measurements, the comparison shows that the performance of the new algorithm is better than that of the traditional, physically-based algorithm. Furthermore, based on the correction algorithm, a new scheme, in which the brightness temperature anomalies at 31.4 GHz and 89 GHz accounting for precipitation effects are directly used as the predictors with those at 54.94 GHz and 55.5 GHz, is developed to estimate TC intensity in the western North Pacific basin. The collocated AMSU-A observations from NOAA-16 with the best track （BT） intensity data from the Japan Meteorological Agency （JMA） in 2002-2003 and in 2004 are used respectively to develop and validate regression coefficients. For the independent validation dataset, the scheme yields 8.4 hPa of the root mean square error and 6.6 hPa of the mean absolute error. For the 81 collocated cases in the western North Pacific basin and for the 24 collocated cases in the Atlantic basin, compared to the BT data, the standard deviations of the estimation differences of the results are 15% and 11% less than those of the CIMSS （Cooperative Institute for Meteorological Satellite Studies, University of Wisconsin-Madison） TC intensity AMSU estimation products.

Retrieval of Upper Tropospheric Relative Humidity by the GMS-5 Water Vapor Channel:A Study of the Technique

This paper presents an analysis of a technique for retrieving upper tropospheric relative humidity through the GMS-5 satellite's 6.7-micron water vapor channel brightness temperature. NCEP analysis shows that a critical assumption of the retrieval theory, namely the constant temperature lapse rate, matches only in the tropical atmosphere. By statistical analyses of brightness temperature simulated by a radiative transfer model and of relative humidity, we examine the effect of lapse rate on this retrieval method and obtain retrieval parameters and error estimates applicable to the GMS-5 satellite over East Asia. If the retrieval parameters are properly chosen, the relative error of retrieving the upper tropospheric relative humidity in this region is less than 10%, and if applied to the low-latitude summer atmosphere, it is less than 5%.

Sea surface wind speed retrieval under rain with the HY-2 microwave radiometer

As rain drops change the radiation and scattering characteristic of the oceans and the atmosphere, the wind speed measuring by spaceborne remote sensors under rainy conditions remains challenging for years. On the basis of a microwave radiometer（RM） loaded on HY-2 satellite, the sensitivity of some brightness temperature（TB）channels to a rain rate and the wind speed are analyzed. Consequently, two TB combinations which show minor sensitivity to rain are obtained. Meanwhile, the sensitivity of the TB combination to the wind speed is even better to the original TB channel. On the basis of these TB combinations, a wind speed retrieval algorithm is developed and compared with Wind Sat all-weather wind speed product, HY-2 RM original wind speed product and buoy in situ data. The wind speed retrieval accuracy is better than 2 m/s for rainy conditions, which is evidently superior to HY-2 RM original product. The applicability of this new algorithm is testified for the wind speed measuring in rainy weather with HY-2 RM.

Microwave Simulations of Precipitation Distribution with Two Radiative Transfer Models

Two microwave radiative transfer models of precipitating cloud are used to simulate the microwave upwelling radiances emerging from precipitating clouds. Comparison of the simulation results shows that significant difference of microwave upwelling radiances exists between these two radiative transfer models. Analysis of these differences in different cloud and precipitation conditions shows that it is complicated but has certain trend for different microwave frequencies. The results may be useful to quantitative rainfall rate retrieval of real precipitating clouds.

Evaluating effects of Dielectric Models on the surface soil moisture retrieval in the Qinghai-Tibet Plateau

Based on the measurement of L-band ground-based microwave radiometer(ELBARA-III type)in the Qinghai-Tibet Plateau and theτ-ωradiative transfer model,this research evaluated the effects of four soil dielectric models,i.e.,Wang-Schmugge,Mironov,Dobson,and Four-phase,on the L-band microwave brightness temperature simulation and soil moisture retrieval.The results show that with the same vegetation and roughness parameterization scheme,the four soil dielectric models display obvious differences in microwave brightness temperature simulation.When the soil moisture is less than 0.23 m3/m3,the simulated microwave brightness temperature in Wang-Schmugge model is significantly different from that of the other three models,with maximum differences of horizontal polarization and vertical polarization reaching 8.0 K and 4.4 K,respectively;when the soil moisture is greater than 0.23 m3/m3,the simulated microwave brightness temperature of Four-phase significantly exceeds that of the other three models;when the soil moisture is saturated,maximum differences in simulated microwave brightness temperature with horizontal polarization and vertical polarization are 6.1 K and 4.8 K respectively,and the four soil dielectric models are more variable in the microwave brightness temperature simulation with horizontal polarization than that with vertical polarization.As for the soil moisture retrieval based on the four dielectric models,the comparison study shows that,under the condition of horizontal polarization,Wang-Schmugge model can reduce the degree of retrieved soil moisture underestimating the observed soil moisture more effectively than other parameterization schemes,while under the condition of vertical polarization,the Mironov model can reduce the degree of retrieved soil moisture overestimating the observed soil moisture.Finally,based on the Wang-Schmugge model and FengYun-3C observation data,the spatial distribution of soil moisture in the study area is retrieved.

Hail Detector and Forecaster ArtAr-HDF

This article describes a new and low-cost microwave passive sensor for hail prediction (forecasting) and detection developed in Armenia, which can be used to implement fully autonomous and automatically functioning hail protection of locally limited or large agricultural and urban areas in order to prevent, suppress or catch hail in traps. The article also presents the results of measurements of the intrinsic emission characteristics of water and ice, rain and hail clouds, carried out in laboratory and field conditions in the Ku-band of radio frequencies. The results obtained showed that the intrinsic emission of a hail cloud in the Ku-band of radio frequencies differs significantly from the intrinsic emission of a rain cloud. The presented results show that indeed the radar is not very suitable for the timely detection and determination of hail with a high probability, which is very important for the timely starting up of anti-hail protection means. On the contrary, radiometers (passive microwave sensors) can become an effective sensing tool for timely detection and recognition of hail with a high probability of long-range approaches up to ~12 - 15 km.