The fourth Sea WiFS intercalibration round-robin experiment (SIR-REX-4),May 1995

This report documents the fourth Sea-viewing Wide Field-of-view Sensor (SeaWiFS) Intercalibration RoundRobin Experiment (SIRREX-4), which was held at the National Institute of Standards and Technology (NIST) on 3–10 May 1995. The agenda for SIRREX-4 was established by a consensus reached at the conclusion of SIRREX-3: there should be an emphasis on training and work to foster and encourage uniform use of accepted protocols for calibrating radiometric instruments in the laboratory. The goal was to host the activity in a setting where proper techniques could be discussed and demonstrated. It seemed appealing to split the day between morning lectures and afternoon laboratory exercises or practicals. The former gave the user community a chance to present what was important to them and discuss it with acknowledged experts in radiometry, while the latter presented a unique opportunity for training and evaluation in the presence of these same experts. The five laboratory sessions were concerned with 1) determining the responsivity of a spectroradiometer and the spectral radiance of an unknown integrating sphere source, 2) demonstrating spectral field calibration procedures for an integrating sphere using three different instruments, 3) measuring spectral radiance using the plaque method, 4) setting up and aligning lamp calibration transfer standards using the NIST specifications for irradiance measurements, and 5) characterizing radiometric instruments. In addition to documenting some supplemental studies performed outside the laboratory sessions, this report includes an evaluation of the hardware that has been used during the SIRREX activities plus a critical evaluation of SIRREX objectives.