For a positive integer k , a {k}-Roman dominating function of a graph G = (V,E) is a function f: V —> {0,1,... ,k} satisfying f(N(v)) ≥ k for each vertex v ε V with f(v) = 0. Every graph G satisfes γ { Rk } (G) ≤ kγ(G) , where γ { Rk } ( G ) denotes the minimum weight of a { k }-Roman dominating function of G and γ(G) is the domination number of G . In this work we study graphs for which the equality is reached, called {k}-Roman graphs. This extends the concept of { k }-Roman trees studied by Wang et al. in 2021 to general graphs. We prove that for every k ≥ 3, the problem of recognizing { k }-Roman graphs is NP-hard, even when restricted to split graphs. We provide partial answers to the question of which split graphs are {2}-Roman: we characterize {2}-Roman split graphs that can be decomposed with respect to the split join operation into two smaller split graphs and classify the { k }-Roman property within two specific families of split graphs that are prime with respect to the split join operation: suns and their complements.

The Remote sensing and Interference detector with radiome-Try and vegetation Analysis (RITA) payload was selected in 2019 the 2nd GRSS Student Grand Challenge to fly onboard AlainSat-1, a 3U CubeSat developed at the National Space Science and Technology Center (NSSTC) in United Arab Emirates. RITA payload includes a passive Microwave Radiometer (MWR), a LoRa transceiver, and an hyper-spectral camera. The objective of the payload is to retrieve Earth Observation (EO) parameters such as: soil moisture, sea-ice thickness and concentration, among others. A Radio Frequency Interference (RFI) detection algorithm is also included to the payload to create interference maps in the received signals.

In 2019, the IEEE 2nd GRSS Student Grand Challenge selected the Remote sensing and Interference detector with radiomeTry and vegetation Analysis (RITA) payload to fly on board of AlainSat-1, a 3U CubeSat from the United Arab Emirates' National Space Science and Technology Center (NSSTC). The RITA payload is equipped with a Commercial Off- The-Shelf (COTS) Software Defined Radio (SDR) for the RF signal conditioning and a System on a Chip (SoC) processor in charge of controlling the execution and processing of each experiment that conforms the payload. RITA includes an L-band microwave radiometer (MWR), a Radio Frequency Interference (RFI) detector, a LoRa transceiver, and a hyper-spectral camera. A multi-level acquisition strategy joining several sensors for the aforementioned experiments' allows this payload retrieve parameters such as: soil moisture derived from the MWR, Normalized Difference Vegetation Index (NVDI) obtained from the hyper-spectral camera, improved acquisition of vegetation-related measurements through the LoRa transceiver, or even the compilation of worldwide interference maps. This manuscript will focus on the design, implementation, verification, and testing of the MWR on board the RITA payload, a successor of previous CubeSat missions such as FSSCat, which carried the FMPL-2 payload, or 3Cat-4 carrying FMPL-1 payload.

FSSCat, the “Federated Satellite Systems/3Cat-5” mission was the winner of the 2017 ESA S^3 (Sentinel Small Satellite) Challenge and overall winner of the Copernicus Masters competition. FSSCat consists of two 6 unit cubesats carrying on board UPC's Flexible Microwave Payload - 2 (FMPL-2), an L-band microwave radiometer and GNSS-Reflectometer implemented in a software defined radio, and Cosine's HyperScout-2 visible and near infrared + thermal infrared hyperspectral imager, enhanced with PhiSat-1, a on board Artificial intelligence experiment for cloud detection. Both spacecrafts include optical and UHF inter-satellite links technology demonstrators, provided by Golbriak Space and UPC, respectively. This paper describes the mission, and the main scientific results of the FMPL-2 obtained during the first three months of the mission, notably the sea ice concentration and thickness, and the downscaled soil moisture products over the Northern hemisphere.

Global change and sea level rise are increasing the interest in monitoring oceans, and specially the Arctic. L-band microwave radiometers can be used for thin sea ice thickness and oceans monitoring, and these maps are being routinely generated from SMOS [1] and SMAP [2], which if combined with imagers provide a higher resolution. The CubeSat-based payload RITA (RadIomeTry and vegetation Analysis) plans to address those monitoring needs by including an IoT enabled payload, a hyperspectral imager and an L-band microwave radiometer with RFI detection and mitigation [3]. The IoT payload implements an SDR-based LoRa modulation and it will be used to perform On-Demand executions of the radiometer and the imager payloads on-board RITA. As part of this work, an in-depth description of the objectives, concept of operations and hardware and software architecture and implementation of the IoT LoRa module will be provided.

The Flexible Microwave Payload -2 is the microwave remote sensing payload of the FSSCat mission. The instrument is the outcome of years of work of the Universitat Politécnica de Catalunya Passive Remote Sensing Laboratory, and the NanoSat-Lab. The FSSCat mission was launched on board the Vega VV16, on September the 3rd, 2020. The instrument was executed for the very first time on September the 16th, 2020, and it was commissioned less than two weeks later. This extended abstract presents the geo-located FMPL-2 measurements, which consist of a Global Navigation Satellite System - Reflectometer and an L-band radiometer. The performance of the instrument and preliminary level 1C results are presented, showing that CubeSats can to perform passive microwave remote sensing scientific missions.

The Remote sensing and Interference detector with radiomeTry and vegetation Analysis (RITA) payload is one of the Remote Sensing payloads selected by the 2nd GRSS Student Grand Challenge in 2019 to fly on board of a 3U satellite that is being developed at the National space Science and Technology Center (NSSTC), United Arab Emirates University. RITA has been designed as an academic mission with a strong focus on Earth Observation techniques and technologies. This payload is equipped with a Software-Defined Radio for microwave radiometry and RFI detection, a hyperspectral camera (25 bands from 600 to 975 nm), and a LoRa transceiver, which will work in tandem to produce vegetation-related measurements with improved accuracy. Soil moisture measurements, for example, will be derived from a Total Power Microwave Radiometer working at L-band and Normalized Difference Vegetation Index (NDVI) measurements in a technique known as Pixel Downscaling. In this work, recent advances in the payload design will be presented, as well as a more in depth mission analysis.

The celebration of the International Polar Year in 2007 remarked the necessity to better monitor the polar regions. Moreover, the H2020 “Operational Network of Individual Observation Nodes” (ONION) project analyzed and proposed an overall EU strategy and technical guidelines to develop and implement innovative Earth Observation concepts in the time frame 2021-2027. The top priority that was identified was the Maritime Weather Forecast, and in particular the Arctic sea ice monitoring use-case. Currently, those needs have been addressed with remote sensing satellites or in-situ instruments. However, in-situ instruments often sink or crash with ice blocks. Additionally, these instruments are isolated, making challenging its deployment and the data retrieval, using LEO satellite communications (e.g. Iridium, OrbComm). This also poses a problem in terms of modularity and flexibility, since sensors rely on proprietary communication systems. This work proposes a modular and cost-effective solution to this problem applying the paradigm of the Internet of Things to this context. Particularly, Long Range (LoRa) is one of the most frequently used and efficient technologies that also ensures long ranges. As part of the presented work, a satellite constellation is proposed, analyzed to cover the Arctic region. The maximum number of sensors simultaneously using the LoRa technology is also evaluated.

The Remote sensing and Interference detector with radiomeTry and vegetation Analysis (RITA) payload is one of the Remote Sensing payloads selected by the 2nd GRSS Student Grand Challenge to fly on board of a 3U satellite from the United Arab Emirates' National Space Science and Technology Center (NSSTC). The main objectives of RITA are to perform microwave radiometry measurements at L-band, vegetation analysis using a hyper-spectral camera, Radio-Frequency Interference (RFI) detection and classification, and a technology demonstration of sensor networks using a custom LoRa transceiver. Radiometry measurements, RFI detection, and the LoRa experiment will be performed using a Software-Defined Radio (SDR) with a frontend designed as a modified version of the Flexible Microwave Payload 1 (FMPL-1) used in the3Cat-4 mission, whereas an hyper-spectral camera will be used primarily for vegetation measurements. This work discusses the description and design of the payload, and emphasizes on the techniques used for the generation of the scientific outcome.

In the last years, the need to access Earth Observation high spatial resolution data with very low latency, ideally in near-real-time, has increased. Distributed Satellite Systems have emerged as an effective and efficient architecture to deal with these tight requirements. One of these systems is the Federated Satellite Systems which explore the benefits of sharing unused and available resources between satellites, such as memory storage or downlink opportunities. This interaction is known as satellite federations. Additional downlink contacts may enable low-latency communications and increase the downlink capacity. Therefore, the deployment of federations would allow satisfying current Earth Observation community demands. This work contributes to establish this promising paradigm by presenting a proof-of-concept of a federated system, called FSS Experiment payload. This payload is boarded into three stratospheric balloons, and it provides them communications means to create federations. The design of the payload, and the flight campaign results are presented in this work. These results demonstrate the feasibility of deploying federations, as well as the benefits of deploying them in future EO missions.

During these years, novel Distributed Satellite Systems (DSS) have addressed the new Earth Observation (EO) requirements (e.g. near-real time access to data, or multi-point observations). One of the DSS proposals is the concept of Federated Satellite System (FSS) which has explored the benefits of sharing available and unused resources between satellite to maximize the system utility. The possibility to use additional downlink opportunities thanks to federations is a resource that could improve current EO missions, and thus achieving the required performance. For that reason, the FSS Experiment payload has been implemented as a FSS proof-of-concept between 6-Unit CubeSats in the FSSCAT mission. This article presents the design, and the test results of this payload demonstrating its feasibility for future EO missions.

Global Navigation Satellite System Reflectometry and L-band microwave radiometry have been used for soil moisture, biomass, and cryosphere studies. Combining both technologies in a low-power and cost-effective solution could largely improve current Earth observations.3Cat-4 mission is a 1-Unit CubeSat technology demonstrator of the Flexible Microwave Payload - 1, a reduced size payload that combines these two technologies. This work presents the objectives of the3Cat-4 mission and the details of the spacecraft architecture and performance. Each spacecraft subsystem is detailed at hardware and software levels. In addition, the presented results indicate that the current spacecraft design will survive the flight conditions (i.e. thermal and structural ones).

The FSSCat mission is a two nano-satellite Earth Observation mission based on 6-unit CubeSats. This paper is focused on the description of one of the remote sensing payloads: the Flexible Microwave Payload 2 (FMPL-2), on board the3Cat-5/A. The payload design is based on a Software Defined Radio, aiming to demonstrate the capabilities of nano-satellites to provide valuable scientific data. Two different instruments are integrated into a single payload: a multi-constellation (GPS and Galileo) Global Navigation Satellite System Reflectometer (GNSS-R), and a Total Power Radiometer (TPR) with Radio Frequency Interference (RFI) detection and mitigation capabilities. This paper presents the payload design, and the tests conducted during the qualification campaign.

The Flexible Microwave Payload 2 (FMPL-2) is a Remote Sensing payload carried on board3Cat-5/A, one of the two 6-unit CubeSats of the FSSCat mission. FMPL-2 is a payload based on a Software Defined Radio (SDR), integrating two instruments in a single platform: a multi-constellation (GPS and Galileo) Global Navigation Satellite System Reflectometer (GNSS-R), and a Total Power Radiometer (TPR) with Radio Frequency Interference (RFI) detection and mitigation capabilities. This paper focuses on the description of the software developed for the platform, with a detailed description on the optimizations used for the two instruments.

FSSCAT is an innovative mission concept consisting of two federated 6U Cubesats in support of the Copernicus Land and Marine Environment services. The first CubeSat carries the Flexible Microwave Payload-2 (FMPL-2), a dual microwave payload (a GNSS-Reflectometer and an L-band radiometer with interference detection/mitigation), and the second one a hyper-spectral optical payload. The combined use of these payloads will allow to measure soil moisture, ice extent, and ice thickness, and to detect melting ponds over ice. FSSCAT also includes radio and optical inter-satellite links to test some of the techniques and technologies for the upcoming satellite federations. FSSCAT will be the precursor of a constellation of federated small satellites for Earth observation achieving high temporal resolution and moderate spatial resolution in a cost-effective manner.

The3Cat-4 mission aims to demonstrate the capabilities of nano-satellites plus the versatility of a Software Defined Radio for passive Earth Observation. Three different microwave payloads are integrated into a single unit CubeSat platform: a multi-constellation (GPS and Galileo) and a dual-band (L1 and L2) Global Navigation Satellite System - Reflectometer receiver, a total power radiometer including a novel Radio Frequency Interference (RFI) detection and mitigation technique, and an Automatic Identification System receiver for vessels tracking. Being able to validate these technologies in a CubeSat enables their fast adoption as hosted payloads or in more performing dedicated platforms in the future. This paper shows a novel approach for embedding multiple passive microwave payloads in a single platform.