# Satellite Microwave Radiometry for the Observation of Land Surfaces: A General Review

## TL;DR

This paper reviews the use of satellite microwave radiometry for observing land surfaces, focusing on soil moisture, snow, and challenges in data retrieval.

## Contribution

The paper provides a comprehensive review of theoretical and practical advancements in microwave radiometry for land surface monitoring.

## Key findings

- Microwave radiometry has advanced significantly since the 1940s, becoming a key tool for Earth observation.
- Current retrieval algorithms rely on radiative transfer theory to model surface variables like soil moisture and snow properties.
- Challenges remain in retrieving accurate data under dense vegetation and melting snow conditions.

## Abstract

The development of passive microwave sensors traces back to Robert Dicke’s pioneering experiments in the 1940s. Since then, microwave radiometry has evolved into a key tool for Earth observation, strengthened by data from multiple satellite missions operating across different wavelengths. This paper reviews the state of the art in microwave radiometry for monitoring land surfaces. After introducing the theoretical foundations underpinning current missions, we present an overview of major satellite instruments. We then examine early theoretical advances in retrieving soil moisture and snow properties, two applications that contributed to the future development of satellite microwave radiometry missions for the observation of surface variables. Particular attention is given to radiative transfer theory and its solutions, which model the effects of roughness, vegetation, and snow cover. These approaches form the basis of today’s retrieval algorithms and remain central to future missions. Subsequent sections highlight the use of passive microwave data for estimating a variety of surface variables, the role of passive microwave in data assimilation systems and forthcoming missions dedicated to land monitoring. The review concludes with key achievements, ongoing challenges, and open issues—such as soil moisture retrieval under dense vegetation or snow property retrieval in melting conditions. Addressing these limitations is critical to fully exploiting microwave radiometry in the context of climate research and mitigation strategies.