Vol.25, NO.6, 2014

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REVIEWS
The Progress on Application of Ensemble Prediction to Flood Forecasting
Zhao Linna, Liu Ying, Dang Haofei, Jiang Di, Duan Qingyun, Wang Binyan, Bai Xuemei, Liang Li
2014, 25(6): 641-653.
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Abstract:

Hydrological Ensemble Prediction is a forming and developing branch of hydrology. Its development can be roughly divided into two stages. The first stage is the longer term streamflow predictions stage from 1970 to the end of the 20th Century, and the second stage is to learn the concept of the numerical weather forecast applied to hydrological ensemble prediction at the beginning of the 21st Century. Compared with the single deterministic prediction meteorological, ensemble numerical forecasting can describe the uncertainly quantitatively. In recent ten years, the application of meteorological ensemble numerical forecasting to hydrological ensemble prediction on the warning of flood forecasting attaches great importance.In addition to single ensemble system, multiple ensemble system is gradually applied to hydrological ensemble forecast, even in some small basins. To study potential benefits of using the TIGGE database in early flood warning, an atmospheric-hydrologic-hydraulic coupled cascade system driven by TIGGE ensemble forecasts is set up. Some hydrological ensemble prediction systems use high resolution ECMWF-EPS or limited area EPS as weather forecasts as initial and boundary conditions. Over the past decade, many studies show that forecasts based on hydrological ensemble prediction systems not only can add accuracy but also increase the warning lead time. The European Flood Alert System and the Advanced Hydrologic Prediction Services of NOAA realize real-time prediction in flood forecast, but there are still some problems, such as large amount of calculation and massive data to handle.The various pre-process and post-process of ensemble forecasts of techniques are in the stage of exploration and verification. Besides, there are a great deal of challenges and difficulties in understanding how to make flood warning decisions based on probabilistic forecasts better.
ARTICLES
Operational Assimilation of Data Retrieved by GNSS Observations into GRAPES_Meso 3DVar System
Wang Jincheng, Gong Jiandong, Deng Liantang
2014, 25(6): 654-668.
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Abstract:
Radio occultation (RO) observations using the Global Navigation Satellite System (GNSS) provides valuable data to support operational numerical weather prediction, and it is proved that the assimilation of RO data has the potential to significantly improve the accuracy of global and regional meteorological analysis and weather prediction. RO observations have many advantages such as high precision, global coverage and high vertical resolution compared with other observations. RO observations provide phase (Level 1a), bending angle (Level 1b), refractivity (Level 2a), retrieved pressure, temperature and humidity profiles (Level 2b), all of which can be assimilated into numerical model. Bending angle and refractivity are proved better choices for assimilation as observation operators are less complicated, and have no disadvantages associated with the modeling of ionospheric effects in the assimilation model. However, assimilation of water vapor, temperature or pressure derived from RO observations have advantages that data forms are same as model variables, and it is proved that assimilation of retrieved data also improve the accuracy of global analyses and forecasts significantly.In the operational GRAPES (Global/Regional Assimilation and Prediction System) regional (GRAPES_Meso) 3-dimensional variational (3DVar) system, the analysis is performed in model vertical level, but it can only assimilate the upper-level wind, pressure and humidity from radiosonde report (TEMP), upper-level wind and humidity by AIREP, cloud drift wind (SATOB), the pressure from surface station report over land (SYNOP) and over sea, integrated column precipitable water vapor (IPW) retrieved by ground-based GPS observations and radar wind profiles. In order to assimilate RO retrieved atmosphere data and address their impacts on analyses and forecasts, observation operators of retrieved humidity and pressur eassimilation are developed first, and then quality control and vertical thinning scheme are formed and discussed. Results of one month experiments show that the assimilation of GNSS/RO retrieved pressure and humidity data have considerable positive impacts on analyses of geopotential height, minor positive impacts on humidity analyses, geopotential height, humidity forecasts, rainfall forecasts, and major positive impacts on rainfall forecast for Qinghai-Tibet region.
Inter-annual Variability of Winter Asia-Pacific Oscillation and Its Relationship with the East Asian Climate Anomalies
Dong Caigui, Zhao Ping, Liu Ge, Chen Junming
2014, 25(6): 669-679.
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Abstract:
Using 1948-2011 NCEP/NCAR monthly reanalysis data and 1951-2010 precipitation data at 160 meteorological stations of China, the empirical orthogonal function (EOF), correlation analysis and composite analysis methods, the winter (December, January and February) atmospheric teleconnection over the Asian-Pacific and its association with East Asian winter monsoon and precipitation are examined. Results show an Asian-Pacific Oscillation (APO) teleconnection in upper-tropospheric temperature disturbance between the Asian-western Pacific and the central-eastern Pacific region during winter, which is similar to the APO phenomenon during summer. When the mid-upper troposphere temperature in mid-lower latitudes of East Asia is warmer, it is colder in mid-lower latitudes of the central and eastern North Pacific, and vice versa. The APO reflects the variability of the zonal thermal contrast between Asia and North Pacific. Compared to summer, the Asian anomalous center of DJF APO is southward and eastward in position. DJF APO index does not show a significant linear trend. The power spectrum analysis shows that the APO index has the varying periods of 2-6 years. Corresponding to a higher APO index, geopotential height disturbance in mid-upper tropospheres is lower in mid-higher latitudes of East Asia and it is higher in mid-higher latitudes of central and eastern North Pacific. Also, there is a "seesaw" in lower latitudes between the Asian-western Pacific region and the central-eastern Pacific, but with a reversed phase comparing to that in higher latitudes. This anomalous feature in geopotential height in the upper troposphere indicates a westward long-wave trough in East Asia and a northward high pressure in the tropics of East Asia, with a deep anti-cyclonic anomaly over southern China. Wind anomalies of northeasterly prevail over southern China in the lower troposphere, with divergence anomalies of water vapor and downward motion anomalies in southern China. Accordingly, the local precipitation decreases. However, these relationships between DJF APO and atmospheric circulation are different from those during summer. Moreover, the APO index is highly correlated with ENSO as well.
Response of Spring Maize Growth Stage to Climate Change in Northeast China over the Past 30 Years
Mu Jia, Zhao Junfang, Guo Jianping
2014, 25(6): 680-689.
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Abstract:
Northeast China is the main producing area of spring maize. Study on the response of spring maize growth stages to climate change has important significance for the agricultural production in Northeast China.Based on observations of spring maize at 55 agricultural meteorological stations, and daily meteorological data of 16 meteorological stations in Northeast China, combined with generally accepted indicators of agricultural meteorology, as well as the law of growth and development of spring maize, significant meteorological factors affecting the spring maize growth are determined at three time scales of inter-annual, potential growing season and crop growth stages. Variations of spring maize growth stages in Northeast China over the past 30 years are analyzed, using methods of trend rate, spearman correlation analysis, principal component analysis and structural equation modeling. Relationships between maize growth stages and climate change are explored. Finally, responses of spring maize growth stages to meteorological factors over the past 30 years are further analyzed at different time scales.The result shows that spring maize critical growth stages in Northeast China over the past 30 years are postponed. Compared to the stage of tasseling, delaying trends at sowing stage and maturation stage are obvious in most areas. The number of days decreases during the early maize growth stages, while both the late maize growth stages and growth stages extend. In most years, the sowing date of spring maize is later than suitable planting date, and the maturating date is earlier than the first frost date, reducing risks. Under climate warming, the late-maturating maize can be expanded in these areas in order to improve the utilization of thermal resource. Responses of spring maize growth stages to temperature factors are the most notable during the past 30 years.The result by principal component analysis shows that the increased temperature at the inter-annual timescale, the prolonged temperature growth period and the high temperature on the crop growth stages are more notable than other meteorological factors. While, in the structural equation modeling, effects of temperature factors on growth stages are partly indirect, and significant meteorological factors can explain 44% of variation in growth stages. Results deepen understanding effects of climate change on crop mechanism, and can be used as scientific basis for adaptation to climate change in the future.
Characteristics of PM2.5 in Beijing and Surrounding Areas from January to March in 2013
Jin Junli, Yan Peng, Ma Zhiqiang, Lin Weili, Liu Ningwei, Ma Jianzhong, Zhang Xiaochun, Jia Xiaofang
2014, 25(6): 690-700.
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Abstract:
Frequent and serious haze and fog events happen from January to March in 2013 in Beijing and surrounding areas under special climate conditions, which are different from those in last decades. 8 haze and fog events during this period are defined in accordance with the meteorological definition. The observational PM2.5, black carbon (BC) concentration and the meteorological data at 8 stations in Beijing, Tianjin, Hebei and Shanxi are used to analyze the fine particle matter and BC pollution level and regional characteristics. The meteorological-parameter variation characteristic and its possible influence on transportation and dilution of atmosphere pollutants are investigated as well.Extraordinarily high daily average PM2.5 concentrations (e.g., 579 μg·m-3 at Shijiazhuang Station) are found, much higher than former researches. Investigations indicate that even though the diurnal variation of PM2.5 concentration varies from station to station, there is a regional high concentration level of PM2.5 in Beijing and surrounding areas for average, which also has characteristic of local accumulation of air pollutants. Analysis on average surface wind speed and atmospheric vertical stability from NCEP reanalysis data in Beijing and surrounding areas from January to March since 2006 to 2013 are conducted, revealing remarkable feature of low surface wind speed and stable structure in lower part of atmosphere in 2013. During the development of fog and haze events, pollution transportation from south to north are observed. High values in south-west and north-east sectors in PM2.5 concentration wind rose correspond to atmospheric-pollutant transportation channel around Beijing.Apart from PM2.5 concentration, BC variation characteristic and its proportion in PM2.5 at Shangdianzi Global Atmosphere Watch Regional Station (SDZ) of Beijing and Gucheng Station (GCH, a rural representative site) of Hebei are studied to enhance the understanding of distinguishing feature of aerosol pollution and its composition in this region. Sharing the similar escalation trend during haze and fog events at both stations, the BC concentration at SDZ is lower, roughly one third of it at GCH. The ratio of BC and PM2.5 mass concentration is of 7.1% during haze and fog events, and 10.3% during the clean days at SDZ. The ratio of BC and PM2.5 mass concentration during haze and fog events versus clean days are of 17.5% and 11.9% at GCH. The contrast values between haze and fog events versus clean days in different stations indicate a higher secondary aerosol proportion during haze and fog events in the down-wind northern area when compared to that in the polluted up-wind southern area in and around Beijing.
The Improvement of FY-3B/VIRR SST Algorithm and Its Accuracy
Wang Sujuan, Cui Peng, Zhang Peng, Ran Maonong, Lu Feng, Wang Weihe
2014, 25(6): 701-710.
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Abstract:
The evolution of sea surface temperature (SST) algorithms is introduced and a set of SST regression formalisms are given. Some improvements are made based on operational SST algorithm from FY-3B meteorological satellite visible and infrared radiometer (VIRR) data. On matching algorithm, quality controlled in situ data from the in situ quality monitor (iQUAM) is used to improve the input data precision of regression. Fields of matchup database (MDB) are enlarged to provide the convenience for error analysis. Pixels with "confident clear" flag in FY-3B/VIRR cloud mask (CLM) products are matched up to form gross matchups, and then tightly filtered by some tests to form tight matchups, which make the sample selection more reasonable. On regression algorithm, based on least-square regression used for the early operational SST product, the robust regression is developed, and its performance is tested by NOAA-19/AVHRR MDB of 2010. It shows that the precision of SST is increased by 21% in daytime with split-window non-linear SST (NL) algorithm and 30% in nighttime with triple-window MC (TC) algorithm. On retrieval algorithm, the spatial uniformity test and climate reference test are introduced, the unidentified cloud (especially at night) is excluded and the SST retrieval precision is improved.A set of SST regression formalisms are tested based on NOAA-19/AVHRR 2010 MDB. It shows NL is the best algorithm for daytime while TC is the best algorithm for nighttime, which is accordant with NESDIS/STAR. The monthly MDB is created from FY-3B/VIRR measurements paired with coincident SST measurements from buoys data.The same regression analysis method is also used on FY-3B/VIRR MDB. Comparing three daytime SST algorithms and five nighttime SST algorithms, the best algorithm to retrieve FY-3B/VIRR SST is NL both in daytime and nighttime. It shows for FY-3B/VIRR nighttime TC, the contribution of 3.7 μm band is smaller than split-window bands, and the calibration of 3.7 μm band has stripe phenomenon. A three-month MDB from October to December in 2012 is used to derive coefficients. An independent MDB from January to March in 2013 is used to access the accuracy of the best NL algorithm for FY-3B/VIRR. Based on matchup analyses, the root mean square error (RMSE) between FY-3B/VIRR SST and in situ SST is 0.41℃ (NL_D) and 0.43℃ (NL_N). Compare with Daily Optimum Interpolation SST (OISST), the RMSE of FY-3B/VIRR SST is 1.45℃ (NL_D) and 1.5℃ (NL_N). When the absolute difference between FY-3B/VIRR SST and OISST is within 2℃, the RMSE is 0.82℃ (NL_D) and 0.84℃ (NL_N).
Environmental Thermal Radiation Interference on Atmospheric Brightness Temperature Measurement with Ground-based K-band Microwave Radiometer
Wang Zhenhui, Li Qing, Chu Yanli, Zhu Yayu
2014, 25(6): 711-721.
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Effects of operating environment thermal radiation interference on atmospheric brightness temperature measurement with ground-based K-band microwave radiometer especially for channels near 28.0 GHz and 30.0 GHz are studied. A model for simulating antenna temperature which expresses the energy received by the radiometer based on radiative transfer is derived and used to calculate the response of the brightness temperature measurements to parameters such as antenna specifications, radome, surrounding temperature and emissivity. Results show that the equivalent main beam efficiency (ηe) defined by 3 dB points is only 73.17% for a typical antenna, of which the half-beam half width α=3.1° and the gain G=30 dB. The value of ηe would be even smaller if factors like aperture radiation effect, shape-error, and occlusion and so on are taken into account. The brightness temperature would fluctuate by 4.0 K in case that ηe=70%, the surrounding temperature and emissivity would change by ΔTg=10 K and Δε=0.05 around Tg=280 K and ε=0.85 if the radome can be neglected. The fluctuation would increase up to 9.6 K if the size of the opening in the radome is just for the main beam. Therefore, if the equivalent main beam efficiency determined by the antenna gain and 3-dB beam width for the current radiometer system is not large enough, variation of the operating environment must be taken into account during the correction of K-band brightness temperature measurement even though LN calibration of the radiometer system can be performed as manual-required. For this, a brightness temperature correction method for operating environment variation is suggested according to the theoretical relationship and the result from application to observations. Over one year application after LN calibration shows that the fitness and correlation between the observed brightness temperature after correction and the calculated brightness temperature with radiative transfer equation is obviously better than before, especially for channels of 28 GHz and 30 GHz.
MODIS/LST Product Validation for Mixed Pixels at Linzhi of Tibet
Wang Yuanyuan, Min Wenbin
2014, 25(6): 722-730.
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Abstract:
Southeastern part of Tibet is featured with complicated terrain and diverse land cover types. Validation of MODIS/LST product (1-km spatial resolution) in this region is faced with mixed pixel issue. Point-based LST measurements cannot represent the pixel well. To obtain ground LST measurements at pixel scale, traditional method usually depends on the high spatial resolution of thermal images, such as Aster and TM. However, these data are often unavailable due to persistent cloud cover and long repeat cycle. Therefore, a new simple method called area-weighted average (AWA) method is proposed, in which land cover map at high spatial resolution is combined with multi-site field observations to model the hypothetical observations at moderate pixel scale. The assumption of AWA method is that field observations can be shared within the same land cover. The AWA method is applied and analyzed on the case of Linzhi (with an area of 20 km2) which locates in southeastern part of Tibet. First, 5 field stations are set up on 5 typical land covers: Grassland, farmland, floodplain, forest at sunny slope, and forest at shadowy slope. The upward and downward long-wave radiations are measured simultaneously. Then the land cover map at 30 m spatial resolution is derived from TM image using maximum likelihood classification method. For every 1-km MODIS pixel, the fraction of each typical land cover is calculated, and the radiation at MODIS pixel-scale is estimated through area-weighted averaging. The broadband emissivity is calculated using linear combination of narrowband emissivity of MODIS band 31 and 32. Finally, LST at MODIS pixel-scale can be calculated based on Stefan-Boltzmann law. The AWA method is used for validating daily product of MODIS/LST from Terra and Aqua platforms on 10 June 2013 (LST at night is used because it changes slowly both in temporal and spatial domain). Results show that the RMSE of MODIS/LST is below 1.4 K (n=30) when applying the AWA method. If a point-based measurement is used to directly represent a MODIS pixel, the RMSE is more than 2.2 K (n=10), showing a tendency of over-estimation. The error of Aqua LST is slightly greater than that of Terra LST, probably due to a larger sensor view zenith angle during overpass. Superiority of the AWA method is more noticeable for pixels with high land cover heterogeneity and gentle terrain. The difference in LST between satellite and field observations can be decreased from 3 K to 1 K. However, for pixels with homogeneous land covers or with very tough terrains, the advantage of AWA method is limited. To further improve the AWA method, terrain adjustment should be taken into account when extrapolating point-based measurements to the same land cover but from another region, because the slope and aspect will influence the surface energy balance process even when the land cover stays the same. Results also indicate MODIS/LST data at nighttime in Linzhi Area are accurate, which are very meaningful considering the low density of meteorological stations in this area.
Determination of Area Precipitation Thresholds of Rainstorm-flood Hazard in the Nandu River Basin
Zhang Yajie, Wu Hui, Wu Sheng'an, Chen Shengbei
2014, 25(6): 731-740.
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Abstract:
Using hydrological model to determine area precipitation thresholds of rainstorm-flood hazard is a tendency of hydrological and meteorological forecast. The Nandu River Basin, locating on the north edge of Hainan Island, is the largest basin of tropical regions in China. And the frequent flood of the Nandu River Basin attracts wide public concern. The HBV (Hydrologiska Byråns Vattenbalansavdelning) model is a semi-distributed conceptual hydrological model with multiple versions, used in more than 40 countries and regions around the world. Using HBV-D model which is suitable for large-scale basin, the basin hydrologic characteristics of the Nandu River Basin are simulated and the area precipitation threshold values are determined. These effects may also provide scientific evidence for early warning in the Nandu River Basin.The model is run in terms of observed daily precipitation, air temperature during 1976-1987 and 2009-2010, and the simulated runoff is verified with corresponding hydrological observations of Longtang Hydrologic Station. Taking 1976-1981 as calibration period, several model sensitivity parameters are selected and calibrated by programming. Periods of 1982-1987 and 2009-2010 are selected for model validating, and the Nash-Sutcliffe efficiency index and correlation coefficient are evaluated. Verifications show that the Nash-Sutcliffe efficiency indexes are 0.891, 0.831 and 0.953, and correlation coefficients are 0.944, 0.912 and 0.977, both passing the test of 0.01 level in 3 periods. It indicates that the model can accurately simulate the Nandu River Basin hydrological characteristics. And it's able to determine area precipitation threshold values of rainstorm-flood hazard in the Nandu River Basin.The curve of stream flow and water level is simulated with historical hydrographic data of 1976-1987 when the water level is greater than or equal to 7 m. Curves of area precipitation and different previous water-levels (7 m, 8 m, 9 m, 10 m and 11 m) are determined by hydrological model HBV-D of the Nandu River Basin. Curves can calculate how many meters the water level will rise when storm comes, in the condition of five previous water-levels. Finally, according to water levels of warning, 10-year return period, 30-year return period and 50-year return period as critical criterions for different warning grades, the area precipitation thresholds in different previous water-levels are determined.The accuracy of area precipitation threshold values are verified using observations of four floods. The result indicates that these values are suitable for forewarning, but the missing of warning is still inevitable. To improve timeliness and accuracy, hourly rolling forecast and early warning can be carried out.
Comparison of the Number of Thunderstorm Days from Lightning Location System and Artificial Observations
Wang Xueliang, Zhang Kejie, Zhang Yijun, Zhu Chuanlin
2014, 25(6): 741-750.
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Abstract:
Using the lightning location system (LLS) monitoring data of Hubei Province from 2007 to 2012 and 1983-2012 artificial observations, 25 meteorological stations with theoretical detection efficiency above 95% are selected to make a relative analysis on the number of thunderstorm days monitored by LLS with different monitoring radius (r) and artificial observations. Results show that annual mean thunderstorm days of artificial observations and LLS monitoring data agree mostly in the radius which range from 6.4 km to 10.2 km. In the circular area when r=7, 8, 9 km, the difference is minimum, with the average difference of about 19%. When r≤7 km, the annual mean thunderstorm days from LLS monitoring data is less than that of artificial observation, while it is more than artificial observation when r≥8 km, and it can replace the number of maximum annual mean thunderstorm days of artificial observations when r=22 km. The ground flash density do not change significantly with the monitoring radius in the range of 2-40 km, the annual mean flash density is 3.9-4.1 times/(km2 ·a) and the average value is 4 times/(km2 ·a) for each monitoring radius. According to data of LLS, 3 methods are suggested to calculate the number of annual mean thunderstorm days of artificial observations. The first method is using the number of annual mean thunderstorm days of LLS monitoring data when r=7 km to represent the artificial observations directly, called direct substitution method. The second method is to calculate the number of annual mean thunderstorm days of artificial observations by the equation with one unknown quantity on the basis of the annual mean flash density data when r=8 km, called ground flash density method. The third method is using the binary equation to calculate the number of annual mean thunderstorm days of artificial observations on the basis of the number of annual mean thunderstorm days and the annual mean flash density data when r=8 km, called binary method. The examination shows that the binary method is the best, followed by the ground flash density method and the direct substitution method. The number of annual mean thunderstorm days of 25 stations calculated by binary method from 2007 to 2012 are equal to that of artificial observations, and the average difference is 7.4%. In 2013, the gap of the number of annual mean thunderstorm days between binary method and artificial observation is 0.8 d, and the average difference is 12.3%.
The Trend and Distribution of Thunderstorm Activity and Influencing Factors in Nagqu Prefecture
Yang Mei, Danzeng Gelie, Dawa Zeren, Bianma Lazhen
2014, 25(6): 751-760.
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Abstract:
Using synoptic meteorology, linear statistical methods and wavelet analysis, thunderstorm data from seven meteorological observatories in Nagqu Prefecture from 1966 to 2011 are analyzed to find the trend and space distribution of the number of thunderstorm days and influencing factors. A significant decreasing trend is found in the number of annual thunderstorm days, and the decreasing rate is around five days per decade. The cause for this trend might be that stronger latitudinal atmospheric circulation and weaker longitudinal circulation in the context of global warming reduces the intensity and frequency of cold air, and the mechanical lifting of moist air, which is not conductive to the formation of thunder clouds. Spatially, there is a deceasing number of thunderstorm days from the north to the south, from high mountainous valleys in the east to plains in the west with the highest number of thunderstorm days in the northeast and the lowest in the southeast. This feature is closely associated with differences in topography, thermal conditions, moisture conditions and climate across the prefecture. Due to high temperatures and strong convective activities in summer, there are significantly more thunderstorm days in spring and fall, and there are less thunderstorm days in winter with cold drying weather and relatively stable atmospheric stratification. As the weather becomes drier in winter, thunderstorms start later and end earlier with a decreasing trend in the period of thunderstorm activity within a year. The inter-annual difference in the number of thunderstorm days mainly depends on the westward move of the subtropical high over the West Pacific Ocean, the position and strength of the ridge line between the east Lake Balkhash high and the Tibetan Plateau high, and the shortwave trough off the Tibetan Plateau. When the west Pacific subtropical high weakens or moves eastward, and the warm moist airflow is prevalent in Nagqu, the number of thunderstorm days is higher. When the west Pacific subtropical high strengthens or moves westward, and the northwest airflow is prevalent in Nagqu, the number of thunderstorm days is lower. Two variation periods of 5-10 years and 20 years are found in the number of mean annual thunderstorm days between May and September. These variations indicate that Nagqu Prefecture will experience a period of a higher number of thunderstorm days.
OPERATIONAL SYSTEMS
Design of Communication Parameters for Beidou Satellite-based Early Warning Information Distribution Method
Gu Junxia, Wang Chunfang, Lin Runsheng, Gao Kang
2014, 25(6): 761-768.
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Abstract:
Beidou satellite-based early warning information distribution (BD-EWID) uses short message service of Beidou Navigation Satellite System to distribute early warning information. BD-EWID effectively improves coverage and timeliness of early warning information distribution in China, especially in marine and distant land areas. However, packet length and service frequency of short message are restricted in Beidou Navigation Satellite System. The data amount of a piece of early warning information often exceeds the transmission capacity of one short message. Therefore, long early warning information must be segmented into multiple smaller packets and sent multiple times. However, the more the packets are, the lower the transmission success rate is, and the longer the whole transmission time is. The existing literature has proposed methods of parallel transmission of uplink terminal and unified message compensation to solve these problems in BD-EWID.Transmission times of early warning information and the number of broadcast ID are two important communication parameters in the method of parallel transmission of uplink terminal and the unified message compensation. The transmission times are closely related to the number of packets and transmission success rate of packets, affect the occupancy rate of channel resource in Beidou Navigation Satellite System. The number of broadcast ID is closely related to transmission timeliness, and affects the scale of the whole system. In order to satisfy demands of transmission success rate of the entire early warning information and transmission timeliness, and to save resource, a new design method of those two communication parameters in BD-EWID is proposed.The design method of two communication parameters is described in detail. The relationship of transmissiontimes, the number of packets and transmission success rate are analyzed. An explicit calculation formula of times of transmission is proposed to obtain the optimal value. The larger the number of packets is, or the higher the transmission success rate is, the more the optimal times of transmission are. Also, the relationship of broadcast ID number, transmission timeliness and transmissiontimes are analyzed. An explicit calculation formula of the number of broadcast ID is proposed to obtain the optimal values. The larger the transmission timeliness is, the smaller the number of broadcast ID is. Finally, optimal results are calculated with the transmission success rate and transceiver delay which are obtained from the experiments. With the increase of the number of packets and transmission success rate, optimal times of transmission increases stepwise. With the increase of transmission timeliness, the optimal number of broadcast ID approximately linearly decreases.The proposed design method of communication parameters can be used as a reference of index calculation in the BD-EWID system design phase.
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