Atmospheric environmental parameters directly affect the earth's ecological environment and climate changes, and even human life and health. For example, aerosols, clouds, and greenhouse gases affect the radiation balance between the sun and the earth through sunlight absorption and scattering, which is an important cause of atmospheric environmental pollution and frequent extreme weather. Additionally, the atmosphere is an aerospace operation area, and environmental parameters such as atmospheric temperature, pressure, density, and atmospheric wind field exert a decisive influence on the design and performance indicators of the equipment. Therefore, the detection of global atmospheric environmental parameters has caught much attention from scholars all over the world.

Satellite remote sensing is an important technical means to obtain global atmospheric environment parameters, and can be divided into active and passive detections. Active detection of its radiation source is to emit different forms of electromagnetic waves to the target. Meanwhile, it does not depend on sunlight and can work day and night. Passive detection of its non-radiation source needs to rely on the reflection of the target object or the electromagnetic wave of the natural radiation source (such as the sun). Compared with the active spaceborne detection technology, the passive detection payloads have a long history, mature technology, and diversified types of remote sensing instruments and detection targets, but there are some problems such as reliance on sunlight, detection time, and regional limitations. The active spaceborne detection technology represented by lidar makes up for these shortcomings, and the active and passive spaceborne remote sensing atmospheric detection technologies are developed jointly to provide strong technical support for the detection of global atmospheric environmental parameters.

Currently, atmospheric environment detection of satellite remote sensing has made great contributions to the detection of clouds, aerosols, atmospheric wind fields, greenhouse gases, temperature, pressure, density, and other parameters, and solved the problems of air pollution, climate changes, and national defense applications. We introduce the development history of spaceborne lidar and focus on the comparative analysis of the advantages and disadvantages of active and passive spaceborne remote sensing payloads for detecting major atmospheric environmental parameters. Finally, the future development trend of atmospheric environmental parameter detection technology in spaceborne lidar and passive remote sensing is summarized.

Since the launch of LITE in the United States, domestic extraterrestrial lidars have developed rapidly for nearly 30 years, and the atmospheric parameters that can be detected mainly include clouds, aerosols, greenhouse gases, and atmospheric wind fields. Although LITE has a short working time, it lays a good foundation for spaceborne lidar atmospheric detection with milestone significance. The ice, cloud, and land elevation satellite (ICESat) carries the geoscience laser altimeter system (GLAS) and is the world's first earth observation laser altimeter satellite. As a follow-up mission to ICESat, the ICESAT-2 satellite is launched by the national aeronautics and space administration of America (NASA) in September 2018, and is equipped with the advanced topographic laser altimeter system (ATLAS) (Fig. 1). Developed by NASA in collaboration with the French National Space Research Center (CNES), CALIOP is a major breakthrough in the development of spaceborne lidar technology and has been in orbit for 17 years now, far exceeding the expected design. Scientific data are provided for such scientific issues as aerosol-cloud-precipitation interactions, global dust distribution, transport and pollution, and studies on weather and climate changes (Fig. 2). As the only lidar system aboard the space station to date, CATS employs photon counting methods to obtain vertical cloud and aerosol distribution characteristics (Fig. 3). To obtain information about the three-dimensional wind field of the global atmosphere, the European Space Agency (ESA) launched the ADM-Aeolus satellite on August 22, 2018, carrying the Atmospheric Laser Doppler Instrument (ALADIN). It is the first Doppler wind measurement lidar to acquire the global atmospheric wind field. This indicates the high precision and strong real-time wind measurement capability of spaceborne lidar and has made great contributions to improving the weather and climate forecasting accuracy, optimizing atmospheric models, and advancing atmospheric dynamics research (Fig. 4). Domestic spaceborne lidar started late. On April 16, 2022, China launched the aerosol and carbon dioxide detection lidar (ACDL) on the atmospheric environmental monitoring satellite (DQ-1). Based on path integral laser differential absorption (IPDA) and high spectral resolution lidar (HSRL) technologies, atmospheric environmental parameters can be obtained, such as global cloud, aerosol vertical profile distribution, and CO₂ column line concentration in full time and with high accuracy. It is also the only on-orbit spaceborne lidar actively detecting greenhouse gases globally (Fig. 5). Spaceborne lidars such as ASCENDS, A-SCOPE, and MERLIN are also based on IPDA. The platforms and main technical parameters of these spaceborne lidar are shown in Table 1.

There are many kinds of passive spaceborne remote sensing for cloud, aerosol, greenhouse gas, and atmospheric wind field loads, and the inversion algorithms are diverse and mature. In 1960, the United States launched the first meteorological satellite TIROS-1 to open a new era of satellite cloud remote sensing observation. The representative of China is the Fengyun meteorological satellite series. The moderate resolution imaging spectroradiometers (MODIS) in the United States launched on the Terra and Aqua satellites and the Himawari series in Japan show good results in cloud remote sensing. There are many kinds of spaceborne passive remote sensing of aerosols and can be roughly divided into the following categories: multi-spectral remote sensing instruments, polarization remote sensing instruments, and multi-angle remote sensing instruments, such as AVHRR, DPC, MODIS, and MISR. In the passive satellite remote sensing of greenhouse gases, the most representative ones are Japan's GOSAT series, the United States' OCO series, and China's GF-5. The atmospheric wind field of passive spaceborne remote sensing mainly takes cloud, water vapor, and atmospheric composition as detection targets for inversion, including MERSI-Ⅱ, AGRI, DPC, MODIS, and AHI.

Satellite remote sensing is an effective means to obtain global atmospheric parameters and provide scientific data support for global environmental and climate changes. The development of passive spaceborne remote sensing starts earlier with more mature technology and more abundant atmospheric environment parameters that can be detected. However, passive remote sensing has inevitable disadvantages, such as low accuracy, incomplete coverage of high latitude areas, and lack of night detection data. As a typical active remote sensing equipment, lidar features high precision and high spatio-temporal resolution, which can make up for the shortcomings of passive remote sensing. At present, ground-based and airborne atmospheric lidar detection has been quite mature, and spaceborne lidar remote sensing detection is the future development trend, which has developed for nearly 30 years since the launch of LITE. The atmospheric parameters that can be detected mainly include clouds, aerosols, greenhouse gases, and atmospheric wind fields. Through comparative analysis, the advantages and disadvantages of active and passive spaceborne remote sensing detection technology of atmospheric environmental parameters are revealed. According to different application scenarios and needs, the appropriate detection methods are chosen.