PDS_VERSION_ID = PDS3 RECORD_TYPE = UNDEFINED ^PDF_DOCUMENT = ("nh_rex_radiometer_calib_v4p7.pdf") MISSION_NAME = "NEW HORIZONS" DATA_SET_ID = "NH-P-REX-2-PLUTO-V2.0" PRODUCER_INSTITUTION_NAME = "SOUTHWEST RESEARCH INSTITUTE" PRODUCT_CREATION_TIME = 2017-09-19T00:00:00 INSTRUMENT_NAME = "RADIO SCIENCE EXPERIMENT" INSTRUMENT_ID = "REX" INSTRUMENT_HOST_NAME = "NEW HORIZONS" OBJECT = PDF_DOCUMENT DOCUMENT_NAME = "REX Radiometer Calibration" PUBLICATION_DATE = 2017-09-19 DOCUMENT_TOPIC_TYPE = "INSTRUMENT DESCRIPTION" INTERCHANGE_FORMAT = BINARY DOCUMENT_FORMAT = "ADOBE PDF" DESCRIPTION = " This document gives details of the REX Radiometer calibration, specifically the combination of in-flight measurements used to determine the System Noise Temperature (SNT) of the Radio hardware used for REX radiometry measurements. It is provided in Draft form only. System Noise Temperature (SNT) is typically measured by injecting known amounts of noise power into the signal path and comparing the total power with the noise injection 'on' against the total power with the noise injection 'off.' That operation is based on the fact that receiver noise power is directly proportional to temperature. Normally, measuring the relative increase in noise power due to the presence of an absolutely calibrated thermal noise source allows direct calculation of SNT. However, for the NH radio subsystem, without an absolutely calibrated thermal noise source, it is possible to calculate the SNT using multiple standard radio sources and Cold Sky: 'on' is when the HGA is pointing at a standard radio source; 'off' is when the HGA is pointing at Cold Sky. There are three Cold Sky locations chosen for NH REX, where the the sky temperature is within a few tenth's of a Kelvin of the Cosmic Microwave Background - CMB - over a section of the sky larger than several times the half-power beam width of the HGA. The primary sources used in the calibration are given in Table 2.01 on page 4 of the document. Using the ratios of radiometry measurements of multiple standard radio sources to radiometry measurements of Cold Sky allows indirect calculation of the SNT, as long as the relative power ratios between the standard radio sources are known and are not unity, and with the following assumptions: 1) we assume that the REX radiometry system response is linear with power. 2) we assume that the maximum signal when the HGA scans across a standard radio source is proportional to the X-band radio flux from that source. The peak in the HGA beam pattern is a significant fraction of a degree, which is much broader than the pointing deadband of 0.1deg used for these observations, so this assumption is reasonable. 3) we assume that the Standard radio sources chosen for this calibration are 'thermal', i.e. they possess blackbody radiation spectra that are constant across the REX band. A note on the draft: in the caption for Figure 2.1.2, the data was taken in July 2016, and downlinked in August 2016. " END_OBJECT = PDF_DOCUMENT END