Electrochemical concentration cell (ECC) ozonesondes flown by NOAA and NASA Wallops Flight Facility (WFF) personnel during the Stratospheric Ozone Intercomparison Campaign (STOIC) conducted at the Jet Propulsion Laboratory's Table Mountain Facility, Wrightwood, California, July 21 to August 1, 1989, exhibited highly similar ozone measurement precisions and accuracies even though considerably different methods were used by the two research groups in preparing the instruments for use and in calibrating the instruments. The Table Mountain data as well as data obtained in the past showed the precisions to range from about ±3 to ±12% in the troposphere, remain relatively constant at ±3% in the stratosphere to 10 mbar, then decrease to about ±10% at 4‐mbar pressure altitude. Corresponding ozone measurement accuracies for individual ozonesonde soundings were estimated to be about ±6% near the ground, decrease to −7 to 17% in the high troposphere where ozone concentrations are low, increase to about ±5% in the low stratosphere and remain so to an altitude of about 10 mbar (∼32 km), then decrease to −14 to 6% at 4 mbar (∼38 km) where ozone concentrations are again low. Stratospheric ozone measurements were also made during STOIC with ground‐based lidars and a microwave radiometer that will be used for ozone measurements in the future at sites of the Network for the Detection of Stratospheric Change (NDSC). The ECC ozonesonde observations provided useful comparison data for evaluating the performance of the lidar and microwave instruments.

The error budget of the Stratospheric Aerosol and Gas Experiment (SAGE) II ozone profile measurements is discussed in depth. Five ozone profiles are compared against coincident ROCOZ‐A and electrochemical concentration cell (ECC) ozonesonde measurements at Natal, Brazil (6°S) and Wallops Island, Virginia (36°N). The mean difference between all the measurements is approximately 1% and the agreement is within 7% at all altitudes between 20 and 53 km. Using datasonde and National Weather Service satellite observations of temperature, the agreement is almost equally as good for ozone mixing ratios on pressure surfaces. A comparison of the intrinsic SAGE II measurement errors with measured tropical variances suggests that the precision of the ozone profiles is approximately 5% between 24 and 36 km, degrading to 7% at an altitude of 48 km. It is inferred that the measurement errors possess a vertical correlation distance of 3 km and that therefore the profile precision improves by a factor of approximately 1.3 if the profiles were to be smoothed over 5 km vertically. The repeatability of SAGE II ozone profiles depends also upon the uncertainty in the profiles' reference altitudes. These errors are correlated over 7‐day periods and increase to 200 m over that period of time. The accuracy of SAGE II ozone profiles is expected to be 6% above 25 km altitude. The SAGE II profiles provide useful ozone information up to approximately 60 km altitude and are more precise than the SAGE I profiles. SAGE II profiles, combined with revised SAGE I profiles, form an excellent data base for estimating the long‐term trend in stratospheric ozone since 1979.

The Alaska earthquake, which occurred at 5:36 P.M. local time on Friday March 27, 1964 (0336, March 28, 1964 UT), initiated a large traveling ionospheric disturbance. This disturbance undoubtedly affected many different types of ionospheric sensors; however, the data reported here are limited to ionosondes operating at College, Alaska; Adak, Alaska; Palo Alto, California; and Maui, Hawaii. The ionosonde data show indications of the perturbation in two different forms. The form depends on the distance between the observing station and the epicenter of the earthquake.

We present an overview of the vicarious calibration of the Sea-Viewing Wide Field-of-view Sensor (SeaWiFS). This program has three components: the calibration of the near-infrared bands so that the atmospheric correction algorithm retrieves the optical properties of maritime aerosols in the open ocean; the calibration of the visible bands against in-water measurements from the Marine Optical Buoy (MOBY); and a calibration-verification program that uses comparisons between SeaWiFS retrievals and globally distributed in situ measurements of water-leaving radiances. This paper describes the procedures as implemented for the third reprocessing of the SeaWiFS global mission data set. The uncertainty in the near-infrared vicarious gain is 0.9%. The uncertainties in the visible-band vicarious gains are 0.3%, corresponding to uncertainties in the water-leaving radiances of approximately 3%. The means of the SeaWiFS/in situ matchup ratios for water-leaving radiances are typically within 5% of unity in Case 1 waters, while chlorophyll a ratios are within 1% of unity. SeaWiFS is the first ocean-color mission to use an extensive and ongoing prelaunch and postlaunch calibration program, and the matchup results demonstrate the benefits of a comprehensive approach.

We present an overview of the calibration of the Sea-viewing Wide Field-of View Sensor (SeaWiFS) from its performance verification at the manufacturer's facility to the completion of its third year of on-orbit measurements. These calibration procedures have three principal parts: a prelaunch radiometric calibration that is traceable to the National Institute of Standards and Technology; the Transfer-to-Orbit Experiment, a set of measurements that determine changes in the instrument's calibration from its manufacture to the start of on-orbit operations; and measurements of the sun and the moon to determine radiometric changes on orbit. To our knowledge, SeaWiFS is the only instrument that uses routine lunar measurements to determine changes in its radiometric sensitivity. On the basis of these methods, the overall uncertainty in the SeaWiFS top-of-the-atmosphere radiances is estimated to be 4-5%. We also show the results of comparison campaigns with aircraft- and ground-based measurements, plus the results of an experiment, called the Southern Ocean Band 8 Gain Study. These results are used to check the calibration of the SeaWiFS bands. To date, they have not been used to change the instrument's prelaunch calibration coefficients. In addition to these procedures, SeaWiFS is a vicariously calibrated instrument for ocean-color measurements. In the vicarious calibration of the SeaWiFS visible bands, the calibration coefficients are modified to force agreement with surface truth measurements from the Marine Optical Buoy, which is moored off the Hawaiian Island of Lanai. This vicarious calibration is described in a companion paper.