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1. Multi-Frequency Passive Remote Sensing of Ice Sheets from L-Band to W-Band

   https://doi.org/10.1109/IGARSS39084.2020.9324374  

   Aksoy, Mustafa; Kar, Rahul; Sugumar, Prethiga; Atrey, Pranjal (September 2020, IGARSS 2020 - 2020 IEEE International Geoscience and Remote Sensing Symposium)

   null (Ed.)

   Multi-frequency microwave radiometer measurements can reveal important subsurface characteristics of ice sheets such as internal temperature, density, grain size and ice thickness, which are critical to understand ice sheet dynamics. This study explores the sensitivity of electromagnetic radiation from ice sheets to these properties across the microwave spectrum, from L-band to W-band. The results indicate that (i) the maximum depth for which surface radiations provide information decreases from >2000 m in L-band to ~3 m in W-band, (ii) seasonal variations in internal temperatures are reflected mostly at frequencies in K a -band and above, (iii) impact of the geothermal heat flux can be observed mainly in L- and S-bands, and (iv) changes in density and grain size properties affect the electromagnetic penetration depth, thus, may influence surface emissions across the entire microwave spectrum. 

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2. Four-year Cosmology Large Angular Scale Surveyor (CLASS) Observations: On-sky Receiver Performance at 40, 90, 150, and 220 GHz Frequency Bands

   https://doi.org/10.3847/1538-4357/ac397c  

   Dahal, Sumit; Appel, John W.; Datta, Rahul; Brewer, Michael K.; Ali, Aamir; Bennett, Charles L.; Bustos, Ricardo; Chan, Manwei; Chuss, David T.; Cleary, Joseph; et al (February 2022, The Astrophysical Journal)

   Abstract The Cosmology Large Angular Scale Surveyor (CLASS) observes the polarized cosmic microwave background (CMB) over the angular scales of 1° ≲ θ ≤ 90° with the aim of characterizing primordial gravitational waves and cosmic reionization. We report on the on-sky performance of the CLASS Q -band (40 GHz), W -band (90 GHz), and dichroic G -band (150/220 GHz) receivers that have been operational at the CLASS site in the Atacama desert since 2016 June, 2018 May, and 2019 September, respectively. We show that the noise-equivalent power measured by the detectors matches the expected noise model based on on-sky optical loading and lab-measured detector parameters. Using Moon, Venus, and Jupiter observations, we obtain power to antenna temperature calibrations and optical efficiencies for the telescopes. From the CMB survey data, we compute instantaneous array noise-equivalent-temperature sensitivities of 22, 19, 23, and 71 μ K cmb s for the 40, 90, 150, and 220 GHz frequency bands, respectively. These noise temperatures refer to white noise amplitudes, which contribute to sky maps at all angular scales. Future papers will assess additional noise sources impacting larger angular scales. 

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3. Sky-brightness measurements in J ,  H , and K s bands at DOME A with NISBM and early results

   https://doi.org/10.1093/mnras/stad775  

   Zhang, Jun; Zhang, Yi-hao; Tang, Qi-Jie; Wang, Jian; Jiang, Peng; Ashley, Michael C; Ji, Tuo; Zhang, Shao-hua; Feng, Qi; Wang, Zhi-yue; et al (March 2023, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT The radiance of sky brightness differs principally with wavelength passband. Atmospheric scattering of sunlight causes the radiation in the near-infrared band. The Antarctic is a singular area of the planet, marked by an unparalleled climate and geographical conditions, including the coldest temperatures and driest climate on Earth, which leads it to be the best candidate site for observing in infrared bands. At present, there are still no measurements of night-sky brightness at DOME A. We have developed the Near-Infrared Sky Brightness Monitor (NISBM) in the J, H, and Ks bands for measurements at DOME A. The instruments were installed at DOME A in 2019 and early results of NIR sky brightness from 2019 January–April have been obtained. The variation of sky background brightness with solar elevation and scanning angle is analysed. The zenith sky flux intensity for the early night at DOME A in the J band is in the 600–1100 μJy arcsec−2 range, that in the H band is between 1100 and 2600 μJy arcsec−2, and that in the Ks band is in the range ∼200–900 μJy arcsec−2. This result shows that the sky brightness in J and H bands is close to that of Ali in China and Mauna Kea in the USA. The sky brightness in the Ks band is much better than that in Ali, China and Mauna Kea, USA. This shows that, from our early results, DOME A is a good site for astronomical observation in the Ks band. 

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4. Beyond the Pixel: Using Patterns and Multiscale Spatial Information to Improve the Retrieval of Precipitation from Spaceborne Passive Microwave Imagers

   https://doi.org/10.1175/JTECH-D-19-0067.1  

   Guilloteau, Clément; Foufoula-Georgiou, Efi (September 2020, Journal of Atmospheric and Oceanic Technology)

   Abstract The quantitative estimation of precipitation from orbiting passive microwave imagers has been performed for more than 30 years. The development of retrieval methods consists of establishing physical or statistical relationships between the brightness temperatures (TBs) measured at frequencies between 5 and 200 GHz and precipitation. Until now, these relationships have essentially been established at the “pixel” level, associating the average precipitation rate inside a predefined area (the pixel) to the collocated multispectral radiometric measurement. This approach considers each pixel as an independent realization of a process and ignores the fact that precipitation is a dynamic variable with rich multiscale spatial and temporal organization. Here we propose to look beyond the pixel values of the TBs and show that useful information for precipitation retrieval can be derived from the variations of the observed TBs in a spatial neighborhood around the pixel of interest. We also show that considering neighboring information allows us to better handle the complex observation geometry of conical-scanning microwave imagers, involving frequency-dependent beamwidths, overlapping fields of view, and large Earth incidence angles. Using spatial convolution filters, we compute “nonlocal” radiometric parameters sensitive to spatial patterns and scale-dependent structures of the TB fields, which are the “geometric signatures” of specific precipitation structures such as convective cells. We demonstrate that using nonlocal radiometric parameters to enrich the spectral information associated to each pixel allows for reduced retrieval uncertainty (reduction of 6%–11% of the mean absolute retrieval error) in a simple k-nearest neighbors retrieval scheme. 

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5. Long-timescale stability in CMB observations at multiple frequencies using front-end polarization modulation

   https://doi.org/10.1117/12.2629723  

   Cleary, Joseph; Datta, Rahul; Appel, John; Bennet, Charles; Chuss, David; Denes Couto, Julliana; Dahal, Sumit; Espinoza, Francisco; Essinger-Hileman, Thomas; Harrington, Kathleen; et al (August 2022, Proceedings Volume 12190, Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy XI)

   Zmuidzinas, Jonas; Gao, Jian-Rong (Ed.)

   The Cosmology Large Angular Scale Surveyor (CLASS) is a telescope array observing the Cosmic Microwave Background (CMB) at frequency bands centered near 40, 90, 150, and 220 GHz. CLASS measures the CMB polarization on the largest angular scales to constrain the inflationary tensor-to-scalar ratio and the optical depth due to reionization. To achieve the long time-scale stability necessary for this measurement from the ground, CLASS utilizes a front-end, variable-delay polarization modulator on each telescope. Here we report on the improvements in stability afforded by front-end modulation using data across all four CLASS frequencies. Across one month of modulated linear polarization data in 2021, CLASS achieved median knee frequencies of 9.1, 29.1, 20.4, and 36.4 mHz for the 40, 90, 150, and 220 GHz observing bands. The knee frequencies are approximately an order of magnitude lower than achieved via CLASS pair-differencing orthogonal detector pairs without modulation. 

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