![\"\"](\"https:\/\/research.reading.ac.uk\/fiduceo\/wp-content\/uploads\/sites\/129\/2019\/07\/tutorial3_image1-1-1024x771.jpg\")
<\/figure>\r\n\r\n\r\n\r\nAs we saw in the first recipe in this series, this diagram is designed to show the sources of uncertainty from their origin through to the uncertainty in the measurand. On the outside of the tree are the effects leading to uncertainty.<\/p>\r\n\r\n\r\n\r\n
Looking at the diagram in more detail, moving clockwise from the top of the diagram:<\/p>\r\n\r\n\r\n\r\n
The green branch details effects that lead to uncertainty in the calibration parameters a_0{}<\/span>, a_1 <\/span> and a_2 <\/span> , which come from harmonisation (see later recipe in this series entitled \u2018harmonisation\u2019 for more details)<\/p>\r\n\r\n\r\n\r\n The blue branch details effects that lead to uncertainty in how well the measurement function describes the true physical state of the measurement process. These effects contribute to the uncertainty in the \u2018plus zero\u2019 term, u(0) <\/span> ; the main assumption here is that the quadratic equation fully represents the instrument response and there is no higher order nonlinearity<\/p>\r\n\r\n\r\n\r\n The dark purple branch shows effects that contribute to the uncertainty in counts seen when looking at the Earth, u(C_E) <\/span> ; these are sources of noise in the detector and amplified and in the digitisation of the signal for transmission purposes. These will create an independent (random) error from pixel to pixel<\/p>\r\n\r\n\r\n\r\n The light purple branch details the effects that lead to uncertainty, u(C_T) <\/span> , in the counts seen when looking at the calibration target. Here again there is noise in the detector and amplifier, and in the digitisation of the signal. Each measurement of the internal calibration target (ICT) will have an independent noise error, but the ICT is only measured once per scan line, giving a structured random effect. We will discuss structured random effects in more detail in a later recipe.<\/p>\r\n\r\n\r\n\r\n