卫星定位理论与方法-第14次课-精度评定

1、 测量与导航工程系导航与定位教研室陈明剑第第1414次课次课 精度评定精度评定 上次课内容取接收机某一初值（X0、Y0、Z0），有 ：其中 e为方向余弦bZZFYYFXXFZYXFtcjj),(00002020200000)()()(),(ZZYYXXZYXFjjjjxjjjjjeXXZZYYXXXXXF)()()()()(222jyjjjjjeYYZZYYXXYYYF)()()()()(222jzjjjjjeZZZZYYXXZZZF)()()()()(222jjjzjyjxtcZYXFbZeYeXe),(0000XSPXj-X当观测有4颗卫星时，j=14，有 ： 当卫星多于4颗时，可以有最小

2、二乘解算jjjzjyjxtcZYXFbZeYeXe),(0000LAX 1111444333222111zyxzyxzyxzyxeeeeeeeeeeeeAbZYXX4440333022201110tcFtcFtcFtcFLLAX1采用迭代法求解，一般二次解得误差方程法方程 未知参数解未知参数的权逆阵m为伪距观测精度，qii是QX的第i行i列元素 LAXVUNX LAUAANTT其中LAAAUNXTT11)(4441332214111)(qqqqqqAAQTX未知参数精度（中误差） iixqmm 参数精度mX取决于观测精度m和系数阵A，而A只与卫星和接收机几何位置有关，同一类接收机m是不变的，不

3、同地区、不同时间、不同卫星的导航解精度也不同，需有一技术指标衡量导航解的精度 211)()(AAPAAQTTx观测值等权：观测值等权：21IP协方差矩阵：协方差矩阵：估值精度有两部分构成估值精度有两部分构成：1、观测值等效误差、观测值等效误差(UERE：user equivalent range error) UERE = URE(User Range Error) + UEE(User Equipment Error) SPS : SA on : URER 25米米 SA off : URER 5米米2、卫星几何结构有关、卫星几何结构有关(GDOP : geometric dilution

4、of precision)lGPS exhibits statistical accuracy distributions because UERE and GDOP are continuously variable.UERE(User Equivalent Range Error) is a measure of the error in the range measurement to each satellite as seen by the receiver.GDOP is a measure of the error contributed by the geometric rel

5、ationship of the satellites as seen by the receiver.Position Accuracyl UERE = URE + UEEURE(User Range Error) is the portion of the UERE allocated to the Space and Control segment.UEE(User Equipment Error) is the portion of the UERE allocated to the user equipment.Therefore, receiver position accurac

6、y must be specified for conditions of DOP and URE.Dynamic positioning accuracy requirements must take into account the effect of vehicle motion as well.l General DOP conditionsPDOP 6, HDOP 4, VDOP 4.5, and TDOP 6Mission PlanningIs Critical to ObtainGood DOPIntuitive Concepts of XDOP3. GPS导航精度评定指标Dil

7、ution Of Precision (DOP)A Measure of The Geometry Of The Visible GPS ConstellationGood DOPPoor DOPPoor GDOPl Results when angles from receiver to the set of SVs used are similarGood GDOPl Angles from receiver to SVs are differentGDOP作用：作用：1、衡量卫星几何结构对精度的影响、衡量卫星几何结构对精度的影响 GDOP变化比变化比URER快快2、最佳选星、最佳选星qG

8、eneral DOP conditionsPDOP 6, HDOP 4, VDOP 4.5, and TDOP 2.How does satellite geometry influence accuracy?A telemetry example (2D):90oShape of areawhich may containtransmitter30oShape of areawhich may containtransmitterReceiverWithout correcting for these errors, we can achieve about a 5m accuracy wi

9、th parallel tracking units (good ones), or 10m with serial tracking units (cheap ones).Several sources of error are very difficult to correct for.Fortunately, the largest error sources can be corrected for using differential processing.With differential processing, we can achieve accuracies of 1m, a

10、nd even centimeter accuracy with the right receiver.GPS Accuracy RelationshipPOSITION ERROR = PDOP X UERE- Depends on Geometry- Depends on satellite position errors, propagation errors, and instrumentation errors0 PDOPmCode Range ResultsAutonomous Position+/- 10 m (30 ft) error (horizontal)+/- 15 m (45 ft) error (vertical)Carrier Phase ResultsMeasuredReducedBaseline or Vector(cm precision)Azimuth = 212o 42 49.8244”Distance = 557.05307 mDelta Elevation= 4 .8751 m X = -408.251 m Y = -84.830 m Z = -369.413 mOR2