The usefulness of ARM data depends upon the ability to make precise and accurate measurements of the critical quantities. The development of a full collection of new instruments for this purpose would require significant lead time. It would also preclude the acquisition of significant data on the time scale (5 to10 years) over which the project hopes to make a contribution to the modeling of climate change.
Therefore, ARM will depend heavily on the early deployment of existing research quality technologies which are currently in use and available. These instruments will then be supplemented and improved over the course of the experiment. It is expected that the natural evolution of technology and experience garnered from ARM itself will motivate general improvement in the observing system. This approach to the deployment of ARM is especially attractive since the measurement technologies developed over the past decade have now reached levels of accuracy adequate for the initial deployment.
This section of the document describes the technologies which have been judged most promising for obtaining the critical measurements. The instrument selection reflects the observing philosophy discussed in the Requirements Section. ARM will rely heavily on multiple measurements to provide a cross-check and verification process for both the equipment and the data. Therefore, the instrument suite will include several complementary approaches to gathering the same experimental quantity. For the radiometric instruments this results in overlapping wavelength coverage. In the meteorological instrumentation it results in a mixture of complementary remote sensing instruments and direct sampling sounding systems.
The following material is divided into three sections that cover the major elements of the observing program: the base site, the extended observing system, and the calibration facility. Each section contains a discussion of the selected instrument complement associated with that element. The sections will also address relevant deployment issues for the varied equipment. A background discussion of the technologies employed by ARM can be found in Appendix B for those who may be unfamiliar with some of this equipment. The appendix includes a description of the state of the art of radiometric and remote sensing based meteorological measurement systems. There is also a brief discussion of surface property measurements.
In several cases reference is made to instruments that are not yet ready to be deployed as part of the initial ARM field experiment. This includes: currently developing technologies that may soon be available for use; rapidly changing technologies that are likely to develop improved instruments; and experimental technologies that will not be practical for some time. Some of these instruments and recommendations concerning their development are contained in this section of the report. However, any instrument development through the program will be an enhancement rather than a necessary pre-condition. Existing technology is fully adequate to allow prompt and effective fielding of ARM.