Memo Review Memo: 372 - An Amplitude Calibration Strategy for ALMA Moreno & Guilloteau, 2002May10 Reviewer: Jeff Mangum Date Received: 2002Sep10 Review: Summary: I enjoyed the breadth of this memo, but thought that it diverged extensively from its title. The point of these diversions is to show how they affect calibration, which makes them valuable additions to this memo. In a number of places in this memo, conclusions are drawn based on incorrect or unsubstantiated facts. A good example is the dismissal of asteroids as absolute amplitude calibrators. In many of these instances the conclusion drawn by the authors is in fact incorrect. In the end, though, I think that this memo will serve as a very good starting point for discussion on the calibration strategy to be used for ALMA. The basic conclusion that flux calibration is a research project for ALMA is absolutely correct. Individual Comments: Section 3.3: Asteroids -- The emission from asteroids is better modeled than the authors indicate. The series of papers by Lagerros, Muller, and collaborators have shown that the emission from many asteroids can be modeled to better than 5% accuracy over the wavelength range from 5 to 200 micron. In the millimeter/submillimeter range, the modeling accuracy is a bit worse, in the range 5-10%. This incorrect analysis also invalidates some of the conclusions in Sections 12.4 and 13. Section 6.1.1: -- It appears that Jbg has also been ignored in Equation 17. -- The partial derivatives listed are only correct for the low-opacity limit. Since this assumption is not made later, in section 6.2.1, where the dual-load uncertainties are considered, the comparison between the two chopper calibration systems is uneven. Section 6.2.1: -- "Accordingly, the absolute calibration with the dual-load method is intrinsically less accurate than the vane calibration technique." This statement is not correct, as it is based on an uneven analysis of the uncertainties inherent in the two load calibration systems considered. Other uncertainties in the semi-transparent vane calibration technique, most notably the uncertainty in the mean atmospheric temperature, dominate. A complete analysis of these uncertainties leads to the opposite conclusion, that the dual-load method is intrinsically *more* accurate than the single-load (of which the semi-transparent vane is one type) method. This incorrect analysis invalidates a number of statements in this regard in the Abstract and in Section 13 Section 11: Flux Scale I do not see the distinction between the "a posteriori" and "ab-initio" methods. If the instrumental gain is stable, then the standard bootstrapping method for flux scaling will be more stable with time.