Given the low level of quantum yield measured in the WFC3 data, neither the QE curves presented in Figure 5.2nor the WFC3 Exposure Time Calculator (ETC)include the effects of quantum yield. The noise distortion from multiple electrons is not large compared to other contributions to the signal-to-noise ratio in the ultraviolet (see Section 9.2). 5.4.3Flat Fields

The dynamic range of a detector is limited either by the full-well capacity of the device or by the analog-to-digital converter (ADC) and gain setting that are used during readout to convert the accumulated charge into data numbers (DN). At the standard UVIS gain of ~1.5 e –/DN, saturation always occurs on chip unless binning is used, in which case saturation of the binned readout pixel can occur in the ADC. (See Section 5.4.6 for the numerical limits on DN and electrons for unbinned and binned readouts.) If saturation occurs on chip, photometric information can be recovered with great accuracy, as described below. If the charge accumulated in a given (binned) readout pixel exceeds the ADC maximum, any additional charge does not result in any further increase in the DN and may, in cases of extreme saturation, result in values of zero. Extreme over-exposure is not expected to cause any long-term damage to the CCDs, so there are no bright-object limits for the WFC3 CCDs. The fraction of WFC3 pixels impacted by cosmic rays varies from 5% to 9% per chip during 1800 sec exposures in SAA-free orbits, providing a basis for assessing the risk that the target(s) in any set of exposures will be compromised. Observers seeking rare or serendipitous objects, as well as transients, may have stringent requirements on how many cosmic rays can be tolerated in an image combination. Assuming cosmic-rays affect 5-9% of a chip in 1800 sec, at least 4-5 images will be needed to ensure that fewer than 100 pixels will be hit in all images of the combination.

ReadablePro

EI2: May expose internal representation by incorporating reference to mutable object (EI_EXPOSE_REP2)

The Garett Ace Apex is priced for knowledgeable enthusiasts, so it isn’t exactly cheap, but you’re getting a very powerful detector for a very appealing price. For a veteran hobbyist or a pro, it’s a great bargain. Figure 5.14: Hot pixel growth for the WFC3/UVIS chip2 detector between anneals from June 2009 to Nov 2022, as measured from CTE-corrected darks. The use of 12 and 20 e-/pix post-flash accounts for the discontinuities in Nov 2012 and Nov 2021, respectively. The grey and white shading marks the monthly anneal periods. HSC: Huge string constants is duplicated across multiple class files (HSC_HUGE_SHARED_STRING_CONSTANT)When you first start out, you'll want a first metal detector that matches your skill level. Getting a complex machine can be overwhelming for beginners, and might actually deter you from maintaining the hobby. The last thing anyone wants is for you to spend money on a machine that is ultimately not a good fit. No matter what kind of items you're interested in searching for when you get started, getting an entry-level detector that's suited for beginners can help keep you remain engaged, find your comfort zone, and grow your skill organically. The MPP CCD also eliminates residual image, a serious problem that has plagued low-signal-level CCD users for many years. Residual image, also known as quantum-efficiency hysteresis, results when the sensor is either overexposed or first powered up. Under these circumstances, electrons trapped at the Si-SiO 2 interface are slowly released into the pixel's potential well. Residual charge may take hours or even days before its level falls below the read-noise floor. Inverting the CCD causes holes to recombine immediately with the trapped residual electrons, eliminating remnant image effects during integration as well as readout. Like all CCDs operated in a low-earth-orbit radiation environment, the WFC3 CCDs are subject to radiation damage by energetic particles trapped in the radiation belts. Ionization damage and displacement damage are two types of impairment caused by protons in silicon. The MPP mode is very effective in mitigating the damage due to ionization, such as the generation of surface dark current due to the creation of new trapping states in the Si-SiO 2interface. Although protons lose only a minor fraction of their total energy via non-ionizing energy loss, lattice displacement damage can cause significant performance degradation in CCDs by decreasing the charge transfer efficiency (CTE), increasing the average dark current, and introducing pixels with very high dark current (hot pixels). Displacement damage to the silicon lattice occurs mostly due to the interaction between low-energy protons and silicon atoms. The generation of phosphorous-vacancy centers introduces an extra level of energy between the conduction band and the valence band of the silicon. As described above, new energy levels in the silicon bandgap increase the dark current as they allow thermally generated charges to reach the conduction band. As a consequence, the dark current of CCDs operated in a radiative environment is predicted to increase with time. When searching for deep treasures of gold and precious metals, the Groundtech Discovery SMR is one of the best metal detectors and is clearly our top choice. This top model represents the absolute latest in deep seeking technology. See a real 3-D picture of your treasure in the ground before you start digging. This model represents the first of a new generation of 3-D treasure locating detectors. Figure 5.2:Quantum efficiency curves of the WFC3 UVIS1 and UVIS2 CCDs based on Goddard DCL measurements corrected (downward) by TV3 measurements (solid). The integrated system throughput of the UVIS detector was measured on-orbit to be higher than ground tests by 5–20%, and the dashed curves shows the QE under the assumption that this entire gain is due to the QE. In reality, some fraction of this gain is likely attributable to other HSTand/or instrument components.