Calibration strategies for millimeter/submillimeter observation instruments.
| dc.contributor.advisor | Reeves Díaz, Rodrigo Andrés | es |
| dc.contributor.author | Basoalto Salazar, Lilian de las Mercedes | es |
| dc.date.accessioned | 2025-05-26T16:07:07Z | |
| dc.date.available | 2025-05-26T16:07:07Z | |
| dc.date.issued | 2025 | |
| dc.description | Tesis presentada para optar al grado de Doctora en Ciencias Físicas. | es |
| dc.description.abstract | Data calibration is a critical process in astronomical observations as it enables the correction of systematic errors and ensures the reliability of measurements. This aspect is particularly crucial in radio-astronomy experiments such as COMAP and LLAMA, which aim to detect faint astronomical signals with high precision. In these projects, both instrumental and observational challenges, including the perturbation of weak signals by the atmosphere and receiving systems, introduce uncertainties that must be understood and mitigated to ensure accurate results. This research focuses on developing calibration strategies for instruments in the millimeter and submillimeter bands, addressing the factors influencing data integrity. The study concentrates on two main components: the COMAP experiment and the LLAMA calibration loads. Within the framework of the LLAMA Project, a Calibration Loads sub-system for the LLAMAradio-telescope was developed and characterized. This ultra-wideband system allows the various single-pixel receivers planned for LLAMA to calibrate their intensity scales in antenna temperature using the Y-factor technique. We have developed a closed-loop temperature control system based on FPGAs, along with ACS control software, which was integrated into the LLAMA middleware to implement thermal monitoring and control for the Calibration Loads. The characterization of the loads included infrared and radiometric measurements performed on both the prototype and the final loads. Infrared measurements demonstrated thermal stability over time, with standard deviations of less than 1°C for all loads. In radiometric measurements, the calculated brightness temperatures exhibited a linear correlation with the physical temperatures evaluated between 40°C and 70°C. Discrepancies between the physical and the brightness temperatures increased with a rise in Tph. For the prototype, in which power was measured with a 93 GHz heterodyne receiver operated alongside an FPGA-based automated system, the percentage difference reached up to 1% in Kelvin scale at 70°C. In the final loads, power was manually determined using a 93 GHz direct detection receiver, the maximum difference was 5% on the Kelvin scale at 70°C, corresponding to one of the large loads. These variations are attributed to the geometric design and thermal properties of the loads. At 70◦C, the stabilization time of the brightness temperature from ambient temperature was 8 minutes for the small load and 17 and 28 minutes for the blue and red large loads, respectively. The loads remained within the allowed error margin of 1%, validating their stability and accuracy as calibration tools. In the context of the COMAP Project, a radiometric and atmospheric study for the OVRO site at COMAP frequencies was executed. The performance of the receiver was evaluated using a series of scans taken on different dates and times. The Y-factor technique was applied to determine the receiver temperature, incorporating spillover and atmospheric emission modeled with the AM radiative transfer model and MERRA-2 atmospheric database. The results showed that TRx remained stable, with 95% of the values falling between 10 and 31 K and a mean of 17.7 K. The system temperature was calculated by adapting the methodology of O’Neil [40], explicitly including the simulated sky temperature from the AM model using the MERRA-2 database. It was observed that Tsys ranged between 28 and 56 K for 95% of the data, showing dependence on PWV and the elevation angle. As expected, conditions of reduced PWV resulted in lower values of Tsys, highlighting the relevance of these factors in the accuracy of the measurements. COMAP’s sensitivity was found to vary between 146 and 260 mK for 95% of the data, with a mean of 203 mK, evaluated at a ∆ν of 2 MHz and a data sampling rate of 20 ms. The temporal stability of the data ranges between 5 and 22 seconds with a mean of 14 seconds, as evaluated through Allan variance, confirming the presence of gain fluctuations in all analyzed files. The aperture efficiency results showed a decrease with increasing frequency, ranging from 0.27 to 0.51 with a mean of 0.38, evaluated at the central frequencies of COMAP. In the observational framework of the COMAP Project, a validation study of the MERRA-2 atmospheric database model was carried out through an atmospheric analysis at the OVRO site on March 25, 2019, at 15:00 GMT. This analysis compared radiometric measurements obtained by the COMAP instrument with atmospheric simulations generated using the AM radiative transfer model based on the MERRA-2 database for the specific date and time. We determined a PWV content of 5.753 mm for that moment, calculated through vertical integration of the layered model provided by the MERRA-2 database. This value was retrieved by executing the AM radiative transfer model using the same dataset with an error of less than 1%. Additionally, we conducted a radiometric study for OVRO on March 25, 2019, between 14:18 and 14:26 UTC. We analyzed the COMAP Level-1 long skydip power data recorded at elevation angles between 30◦ and 86.5◦ during this period and estimated its atmospheric brightness temperature at different elevation angles. We compared the derived radiometric temperature with simulations from the AM radiative transfer software, based on the MERRA-2 atmospheric database model, and found strong consistency. During the data processing, we observed an excess temperature when the elevation angle decreased, which could be attributed to spillover effects. This excess temperature ranged between approximately 6 K and 8 K at an azimuthal angle of-30◦. As a key scientific outcome of this atmospheric study at the OVRO site, a zenith opacity spectrum was obtained by fitting brightness temperature data across the entire COMAP frequency range, revealing excellent agreement with simulations, with a percent error of only 4%. The same procedure was applied to a more restricted subset of skydip power data, spanning elevation angles between 40◦ and 60◦ within the same evaluated file. The percent error between the calculated and simulated zenith atmospheric opacity is only 4.4%, confirming that short skydips can effectively characterize atmospheric contributions. | en |
| dc.description.campus | Concepción | es |
| dc.description.departamento | Departamento de Astronomía | es |
| dc.description.facultad | Facultad de Ciencias Físicas y Matemáticas | es |
| dc.identifier.uri | https://repositorio.udec.cl/handle/11594/12672 | |
| dc.language.iso | en | en |
| dc.publisher | Universidad de Concepción | es |
| dc.rights | CC BY-NC-ND 4.0 DEED Attribution-NonCommercial-NoDerivs 4.0 International | en |
| dc.rights.uri | https://creativecommons.org/licenses/by-nc-nd/4.0/ | |
| dc.subject | Physical instruments | en |
| dc.subject | Astronomical instruments | en |
| dc.subject | Calibration | en |
| dc.subject.ods | INDUSTRIA, innovación, infraestructura | es |
| dc.title | Calibration strategies for millimeter/submillimeter observation instruments. | en |
| dc.type | Thesis | en |