One of challenging problems in estimating Total Electron Content (TEC) using the dual-frequency GPS observations is to remove the satellite and receiver instrumental biases. This paper proposes a new algorithm, for estimating the satellite and receiver instrumental biases as well as the TEC at GPS station, using dual GPS data, and this algorithm based on gradient model is used to calculate the Satellite-Plus-Receiver (SPR) differential delays in DGPS stations in Hong Kong area. The arithmetic mean of the SPR differential delay estimates over all 25 GPS satellites over the 11 days are 4.34±0.44 TECU（1.52±0.15 ns）, 37.32±0.47 TECU(13.08±0.16 ns) at Kau Yi Chou station and Fanling station respectively. The GPS satellite biases are in the range -5.34 TECU(-1.87 ns) to +9.36 TECU(3.28 ns). The standard deviation of estimated satellite differential delay bias differences between the values determined by Jet Propulsion Laboratory and other organizations is generally about 2.8 TECU(1.0 ns) level. Without calibrating for this SPR differential delay, it is impossible to obtain precise TEC and ionospheric delay estimation from GPS measurements.%单频GPS接收机用户通常需要进行电离层延迟改正,电离层延迟改正量通常来源于电离层延迟改正模型或双频GPS 基准站信息,后者即是利用双频GPS观测值估计电子含量总数,求解电离层延迟改正量.利用双频GPS观测值估计电子含量总数,一个关键问题是去掉卫星与接收机信号延迟偏差.本文提出了一种新方法,采用梯度模型拟合区域电离层电子含量.这种方法应用于香港地区GPS差分台站,利用11天GPS连续观测结果估算了交椅洲和粉岭两个GPS差分台站的卫星与接收机信号延迟偏差,其结果分别为4.34 TECU(1.52 ns)±0.44 TECU(0.15 ns)和37.32 TECU(13.08 ns)±0.47 TECU(0.16 ns).GPS卫星信号延迟偏差在-5.34 TECU(-1.87 ns)至9.36 TECU(3.28 ns)范围之内,其标准差为1.74TECU(0.61 ns),本文方法估算的卫星信号延迟偏差与JPL,UNSW及AG等组织求出的卫星信号延迟偏差值符合度大约为1.0 ns水平通常认为GPS卫星所发射的双频信号是严格同步的,但实际上双频信号在发射时间上存在差异,这种差异称卫星L1/L2信号延迟偏差,或者称卫星延迟偏差.同样,对GPS接收机来说,接收L1,L2信号也存在一信号延迟偏差(因为L1,L2信号必须在接收机中通过不同的硬件路径和电子线路),称接收机L1/L2信号延迟偏差或者称接收机延迟偏差.卫星L1/L2与接收机L1/L2信号延迟偏差之和又简称为卫星与接收机信号延迟偏差.
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