The primary services of the Global Navigation Satellite System (GNSS) are positioning, navigation, and timing. Besides, many other applications, including GNSS RS, have been introduced in recent decades. Measurements made by GNSS RS techniques provide valuable information about different components of the Earth system. Observations of the GNSS signals passing through the atmosphere have been employed to study the atmospheric layers and their variabilities [12; 13]. GNSS signals after reflection from the Earth's surface can also provide information about the reflecting surface. These reflections have been used to study various parameters of the Earth's surface and water cycles, such as snow depth [14], ice height and sea level [15], soil moisture [16], vegetation [17], flood [11; 18], ocean eddies [19], wind speed [20], salinity [21], etc. Global Navigation Satellite System Reflectometry (GNSS-R) is an innovative technique aimed at deriving geophysical parameters by analyzing GNSS signals reflected off the Earth's surface in a bistatic geometry. This technique is an efficient microwave remote sensing approach that utilizes transmitted navigation signals as sources of opportunity. Numerous GNSS satellites, including GPS, Galileo, GLONASS, and Bei-Dou/Compass, are currently transmitting navigation signals based on spread-spectrum technology. Thus, a constellation of GNSS-R small satellites, at a lower cost compared to ordinary RS satellites, can provide a much shorter revisit time using low-cost, low-power passive sensors. Many earlier studies have introduced the applications of GNSS-R on the oceans, land, and ice [22; 23; 24]. The soil moisture, surface roughness, vegetation, and topography are parameters which affect microwave signals. GNSS-R signals as a bistatic radar are also affected by those parameters [25]. However, GNSS signals are at the L-band, which is ideal for soil moisture and surface water remote sensing due to the higher capacity to penetrate vegetation compared to shorter wavelengths [16]. In addition, this technique uses the bistatic configuration, which has a lower sensitivity to surface roughness relative to monostatic [26]. The signals reflected off the surface have a direct relation with surface water and moisture content [11]. For example, the rise of soil moisture leads to increase the signal strength. Using this mechanism could contribute to detecting soil saturation, flooded area, and inland water. The Cyclone Global Navigation Satellite System (CYGNSS) mission is a constellation of eight microsatellites, each with a GNSS-R receiver onboard. The receiver can track and process four GPS signals simultaneously. The tracked GPS L1 C/A signals after reflection from the Earth's surface are used to produce Delay Doppler Maps (DDMs). The overall median revisit time is 2.8 h, and the mean revisit time is 7.2 h [27]. Theoretically, the footprint of reflection received by CYGNSS is nearly 0.5 km \(\times\) 0.5 km. For the ocean, which has a very rough surface, the spatial resolution is approximately 25 km \(\times\) 25 km [28; 29]. Table 1 shows CYGNSS microsatellite parameters retrieved from [16; 23]. The main mission of CYGNSS is to measure the ocean surface wind speed in hurricanes and tropical cyclones, so a relatively low orbital inclination was designed for the satellites. CYGNSS continuously makes measurements over the oceans and provides useful information over the land [29]. CYGNSS offers distinct features compared to other remote sensing techniques such as optical and active monostatic radar. It uses a passive sensor at the L-band frequency wave, which works in all weather conditions regardless of the time of the day, i.e., it can penetrate clouds, fog, rain, storms, and vegetation, and works at night, unlike optical sensors. The CYGNSS constellation of eight microsatellites provides a relatively short revisit time with global coverage over equatorial regions. The products of CYGNSS are publicly available over the oceans and land.