NDACC Complementary Measurements Protocol

There exists mounting evidence that the Earth's ozone layer is changing on a nearly global scale. Although the most pronounced decreases are presently limited in geographic extent to latitudes outside of the equatorial belt and exhibit significant seasonal variability, the findings have sparked intense scientific interest in a worldwide network for the measurement of stratospheric change. The Network for the Detection of Stratospheric Change (NDSC) now the Network for the Detection of Atmospheric Composition Change (NDACC) is a response to that interest. The NDACC is a set of high-quality remote-sounding research stations for observing and understanding the physical and chemical state of the stratosphere. Its efforts are complementary to other existing measurement activities (such as the Global Ozone Observing System, GO3OS), measurements at secondary stations, and satellite data.

The primary goal of the Network is to make the observations through which changes in the physical and chemical state of the stratosphere can be determined and understood. This dual long-term objective of observation and understanding, thus, requires high precision state-of-the-art measurements not just of ozone, but also of a broad range of chemical species and dynamical tracers that influence ozone. On a shorter time-scale, the NDACC aims to provide independent calibration for satellite sensors and to produce a useful data set for testing and improving stratospheric models.

Instrument development and testing is well underway, and current plans call for the operation of at least five primary stations worldwide (some of which are composite sites). Details on the types of instrumentation planned for deployment and the current list of selected primary stations can be found in the NDACC informational brochure (dated June, 1992). It is hoped that a five-station network will be fully operational in the 1993/94 time-frame. As the NDACC has arisen from the interest and involvement of individual scientists within the international scientific community engaged in stratospheric research, its long-term success depends on the continued involvement and expansion in that community. Important organizational impetus and preliminary funding for the NDACC has been provided by such international scientific organizations as the CNRS in France, DSIR in New Zealand, NASA and NOAA in the United States, and by the chemical industry. Support has now broadened to include nearly 30 international scientific organizations. Official endorsement of the NDACC has been received from the United Nations Environment Programme (UNEP) and the International Ozone Commission (IOC) of the International Association of Meteorology and Atmospheric Physics. The Network has also been endorsed by the World Meteorological Organization (WMO) as a major contributor of WMO's Global Ozone Observing System (GO3OS) within the framework of its Global Atmosphere Watch (GAW).

It is clear that the NDACC represents one of several means of obtaining information on stratospheric trends and processes. For example, the Dobson and Brewer measurement networks have each achieved notable success in discerning recent changes in total ozone column abundance. In addition, while the NDACC instrument complement includes UV/Visible spectrographs for measurements of NO2 and other species, visible absorption measurements of NO2 are underway with other instruments at several NDACC and non-NDACC locations. Comparison of NDACC instruments with others will likely improve scientific understanding associated with making and interpreting such measurements as well as broaden their geographical base. In order to improve and foster scientific interaction for investigations of mutual interest and scientific benefit, a protocol has been developed for complementary measurements in the NDACC. Complementary measurement activities should have a specific benefit to the NDACC through, for example, geographical location, measurement technique, or added science value (which could include such aspects as the measurement of additional molecules or parameters).

Complementary measurements could include either long-term or campaign-style observations, and may be conducted from a range of platforms including ground, aircraft, balloon, and satellite. In the case of long-term measurements, commitment must be of sufficient length to allow for adequate trend determination. Since the NDACC is dedicated to the pursuit of measurements of the highest quality, it is necessary for complementary measurements to meet similar standards. Thus, the candidate Complementary Investigator must provide information on the details of the measurement, a record of intercomparison with other measurements, and a description of quality control procedures. In addition, the specific benefit of the measurement to the goals and objectives of the NDACC should be described and the NDACC Data Protocol adopted.

A Complementary Investigator, or CI, is a scientist who: (i) measures one or more stratospheric molecules or parameters of interest to the NDACC (either at their own site or as a visitor at an NDACC site), (ii) has submitted a written statement of interest in pursuing an active collaboration with the NDACC, (iii) has been selected by the NDACC Steering Committee for CI status following the evaluation procedure described below, and (iv) has secured the necessary resources for conducting the measurements and analyzing the data from the CI's own institution or from a specific funding agency.

Scientists wishing to participate in the NDACC as complementary investigators should submit descriptions of their instruments, measurements, and analysis methods along with an outline of their proposed interaction. Such proposals should be brief and be submitted to the NDACC Steering Committee for assigned evaluation. The NDACC evaluation will be conducted as follows:

1. In the case where the complementary measurement technique is that of one of the NDACC primary instrument types (microwave, infrared, UV/Visible, lidar), the proposal shall be evaluated by that NDACC Principal Investigator (PI) instrument subgroup and approved by the Steering Committee.
2. In the case where the complementary measurement technique is different from that of the NDACC instruments, the proposal shall be evaluated by appropriate subgroups of the NDACC Science Team and approved by the Steering Committee.
3. In the case where the complementary measurement is proposed to be conducted at an NDACC site, the proposal must be approved by a committee consisting of those NDACC PIs making measurements at that site, as well as by the Steering Committee.
4. For cases not directly covered under items 1, 2, or 3 above, the NDACC Steering Committee shall decide on an appropriate evaluation procedure.

If the proposing investigator requires specific resources in support of the complementary measurement activity, the proposal should also be submitted by the investigator to the appropriate funding agency. In such cases, a "point of contact" within the agency should be identified in the proposal submitted to the NDACC Steering Committee so that the results of the NDACC evaluation can be communicated to the funding agency.

1. In all cases where the complementary measurement quantity is also measured by NDACC instruments, a strict 'double-blind" intercomparison must be carried out. This may be achieved using an independent method (e.g., sondes vs. lidar ozone observations), an existing record of intercomparison, or with NDACC mobile intercomparators.

2. For the time-frame of measurement acquisition, the CIs shall have access to the archived preliminary analyses in the same manner as NDACC PIs and be bound by the Data Protocol for the submission of their own data during the period of complementary measurement. The CIs are encouraged to collaborate actively with others to ensure their full participation in the analysis / verification process.

3. The NDACC Data Protocol regarding co-authorship and exchange of results will establish the guidelines for collaborative projects.

4. The CI may propose an interaction with the NDACC for a specified period of time (e.g., for a particular campaign), or for open-ended studies.