A transform-domain, instrumentation Global Positioning System (GPS) receiver is developed for high-fidelity signal quality monitoring (SQM), GPS anomalous event monitoring (GAEM), and GPS software-defined radio (SDR) research. Features of the receiver include: a radio frequency front-end with 24 MHz bandwidth on the GPS L1 (1575.42 MHz) and L2 (1227.6 MHz) frequencies with 14-bit sampling capability to capture and analyze high-dynamic-range signals such as in-band interference; An integrated GPS/Inertial Measurement Unit (IMU) data collection capability at 105 Mbytes/sec sustained transfer rate and 2-Terabyte capacity, with a novel, sub-microsecond resolution IMU time stamping method that significantly simplifies GPS/IMU deeply-integrated processing; a continuous-processing transform-domain engine that computes 1024-point complex parallel-code-correlation functions in less than 15 microseconds for 1-ms blocks of data; A runtime-configurable serial engine containing several hundred ‘split-sum’ coarse/acquisition (C/A) code correlators operating on 14-bit input samples; A realtime transform-domain GPS receiver with full message decoding, range measurement, and position-velocity-time solution updates up to a 1 kHz rate. The receiver’s graphical user interface allows runtime interaction via a set of software controls, and realtime internal-parameter graphing capabilities similar in function to a combined digital storage oscilloscope and spectrum analyzer. High-fidelity capabilities of the receiver include 55 points per C/A-chip SQM, and 10-correlator Precise-code SQM. The instrument’s unique GPS/IMU interleaved data collection capability enabled a flight test where GPS carrier phase tracking was maintained for signals with carrier-to-noise ratios (CNR) at the 15 dB-Hz level. The receiver’s application layer is built using a custom-developed, object-oriented applications programming interface that supports customization to suit a variety of applications. The instrument’s capability is demonstrated using two case studies: 1) A realtime indoor GPS reacquisition application performs 1.2-second coherent signal integration to reacquire signals with CNRs at the 15 dB-Hz level. 2) Three remote-controlled continuously-operating GAEM systems installed at three geographically-diverse locations, including one at a prototype Local Area Augmentation System (LAAS) installation at the Memphis International airport, have provided, and are continuing to provide, SDR data records containing real-world GPS anomalous events which are helping to better-understand and design GPS monitors for safety-of-life applications such as LAAS.